全文获取类型
收费全文 | 1652篇 |
免费 | 31篇 |
国内免费 | 186篇 |
专业分类
电工技术 | 24篇 |
综合类 | 15篇 |
化学工业 | 202篇 |
金属工艺 | 67篇 |
机械仪表 | 65篇 |
建筑科学 | 140篇 |
矿业工程 | 12篇 |
能源动力 | 100篇 |
轻工业 | 381篇 |
水利工程 | 31篇 |
石油天然气 | 69篇 |
武器工业 | 2篇 |
无线电 | 49篇 |
一般工业技术 | 440篇 |
冶金工业 | 37篇 |
原子能技术 | 8篇 |
自动化技术 | 227篇 |
出版年
2024年 | 2篇 |
2023年 | 15篇 |
2022年 | 16篇 |
2021年 | 15篇 |
2020年 | 10篇 |
2019年 | 34篇 |
2018年 | 35篇 |
2017年 | 31篇 |
2016年 | 30篇 |
2015年 | 35篇 |
2014年 | 29篇 |
2013年 | 22篇 |
2012年 | 171篇 |
2011年 | 177篇 |
2010年 | 89篇 |
2009年 | 60篇 |
2008年 | 198篇 |
2007年 | 218篇 |
2006年 | 100篇 |
2005年 | 86篇 |
2004年 | 77篇 |
2003年 | 69篇 |
2002年 | 73篇 |
2001年 | 83篇 |
2000年 | 66篇 |
1999年 | 32篇 |
1998年 | 15篇 |
1997年 | 19篇 |
1996年 | 14篇 |
1995年 | 5篇 |
1994年 | 4篇 |
1993年 | 3篇 |
1992年 | 2篇 |
1991年 | 3篇 |
1990年 | 3篇 |
1989年 | 3篇 |
1988年 | 1篇 |
1987年 | 3篇 |
1986年 | 3篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1983年 | 5篇 |
1982年 | 2篇 |
1981年 | 1篇 |
1980年 | 2篇 |
1979年 | 1篇 |
1974年 | 2篇 |
1973年 | 1篇 |
1965年 | 1篇 |
1964年 | 1篇 |
排序方式: 共有1869条查询结果,搜索用时 15 毫秒
81.
Gai MN Ferj S García E Seitz C Thielemann AM Andonaegui MT 《Drug development and industrial pharmacy》1999,25(2):131-140
Two sustained-release (SR) lithium carbonate (Li) matrix tablets, which use a hydrophilic (HP) matrix of hydroxypropylmethylcellulose (Methocel 4K MP) and a lipid (L) matrix of hydrogenated castor oil (Cutina HR) as sustaining agents, have been studied. In vitro performance through dissolution tests in different media was established. The L and HP formulations were affected by the composition of the dissolution media, and liberation was complete in 8 hr using a variable-pH medium that simulates the gastrointestinal (Gl) pH. Liberation was better described by the diffusional model of the square root of time for the L matrix and by zero-order kinetics for the HP matrix. Absolute bioavailability (BA) and food-induced changes on BA of both formulations were studied. The in vivo study design was a 4 x 4 Latin square involving 12 subjects who received two tablets of a 300-mg dose of SR formulations while fasting or with a standardized normal, high-fat, or high-fat/high-protein meal. The results for both formulations showed no differences in the disposition parameters and mean residence time when the tablets were administered with any type of diet. Changes in rate of absorption were found when both types of tablets were administered with any class of diet. The analysis of the ratio Cmax/AUC (area under the curve) evidenced that changes in Cmax were attributable to a higher rate of absorption for the HP matrix and to a higher amount absorbed for the L matrix. In the last, high-fat and high-fat/high-protein diets produced higher AUCs than under fasting condition. The SR Li tablets formulated with hydrogenated castor oil were affected more by high-fat food, probably because of the increase of pancreatic and biliary secretions promoted by the meal, which would affect the matrix itself. The HP matrix was also affected, but to a lesser extent. The magnitude of the change in Cmax observed with this matrix probably is not important from a clinical point of view. Absolute BA was very low for the lipid matrix; in addition, since it is more seriously affected by food, probably it is not a good choice for a drug such as lithium. The in vivo behavior of the HP matrix makes it advisable to invest in efforts to achieve increased BA. Comparing in vitro and in vivo results, the focus should be achieving sustained, but complete, in vitro liberation in not more than 3 hr, with simulation of the transit time through the stomach and small bowel since lithium ion is only absorbed to this point. 相似文献
82.
Exposure of gold surfaces to solutions of dithiobis N-succinimidyl propionate (DTSP) gives rise to the modification of the surface with N-succinimidyl-3-thiopropionate (NSTP) which can, in turn, react with amino groups allowing for the covalent immobilization of enzymes such as horseradish peroxidase (HRP). The coverage of NSTP has been estimated to be of the order of 1.3 x 10(-10) from the charge consumed during its reductive desorption. The binding reaction of HRP with NSTP modified gold surfaces has been studied with the quartz crystal microbalance, and the results suggest that the immobilization process involves two steps in which the first (faster) appears to correspond to the rapid incorporation of the enzyme whereas the second is likely due to the slow incorporation of additional enzyme and/or reorganization of the immobilized layer. Spectrophotometric and electrochemical assays indicate that the immobilized HRP retains its enzymatic activity after immobilization onto the DTSP modified gold surface. The amount of immobilized (and active) HRP was estimated from QCM and spectrophotometric measurements to be of the order of 1.5 x 10(-11) mol/cm2. A peroxide biosensor was developed making use of a gold surface modified with DTSP and HRP employing Os and Ru complexes of 1,10-phenanthroline 5,6-dione (phen-dione) of the type [M(phendione)x(L)3-x]+2 (where L = 1,10-phenanthroline or 2,2'-bipyridine, x = 1-3) as mediators with the quinone moieties being the active component. The efficiency of the mediators increased with increasing number of phendione ligands. 相似文献
83.
Arrangements are described for the recording of volume holograms with two sections that, when stacked together, work as uniaxial centered lenses and allow one to solve the problem of angular selectivity in the imaging of wide objects. The performance of such systems is examined qualitatively, and suggestions aimed at improving these designs are proposed. 相似文献
84.
We show that a temporal effect equivalent to the spatial Talbot effect (self-imaging) applies to the reflection of periodic pulse trains from linearly chirped fiber gratings (LCFG's). For specific input repetition periods the reflected signal is an exact replica of the input signal. Input repetition period values that give rise to this effect depend on the dispersion coefficient of the grating. We propose to use this effect as an alternative for dispersion measurement in LCFG's. Furthermore, by using the properties of the temporal Talbot effect, we can design linear passive devices (LCFG's) for use as frequency multipliers, able to multiply the repetition rate of a given pulse train. 相似文献
85.
<正> 本文介绍了一种旋风分离器的快速设计方法,该法可提供最佳设计结构,并考虑到固体粒子密度。虽然使用了试差法,但仅经几次试差即收敛。 相似文献
86.
González-Coloma A Reina M Medinaveitia A Guadaño A Santana O Martínez-Díaz R Ruiz-Mesía L Alva A Grandez M Díaz R Gavín JA De la Fuente G 《Journal of chemical ecology》2004,30(7):1393-1408
We have tested the insect antifeedant and toxic activity of 43 norditerpenoid alkaloids on Spodoptera littoralis and Leptinotarsa decemlineata including eserine (physostigmine), anabasine, and atropine. Antifeedant effects of the test compounds were structure- and species-dependent. The most active antifeedants to L. decemlineata were 1,14-diacetylcardiopetaline (9) and 18-hydroxy- 14-O-methylgadesine (33), followed by 8-O-methylconsolarine (12), 14-O-acetyldelectinine (27), karakoline (7), cardiopetaline (8), 18-O-demethylpubescenine (13), 14-O-acetyldeltatsine (18), takaosamine (21), ajadine (24), and 8-O-methylcolumbianine (6) (EC50 < 1 microg/cm2). This insect showed a moderate response to atropine. S. littoralis had the strongest antifeedant response to 24, 18, 14-O-acetyldelcosine (19), and delphatine (29) (EC50 < 3 microg/cm2). None of the model substances affected the feeding behavior of this insect. The most toxic compound to L. decemlineata was aconitine (1), followed by cardiopetalidine (10) (% mortality > 60), 14-deacetylpubescenine (14), 18-O-benzoyl-18-O-demethyl-14-O-deacetylpubescenine (17), 14-O-acetyldelcosine (19), 14-deacetylajadine (25) and methyllycaconitine (30) (% mortality > 45). Orally injected S. littoralis larvae were negatively affected by 1, cardiopetaline (8), 10, 1,14-O-acetylcardiopetalidina (11), 12, 14, 1,18-O-diacetyl-19-oxo-gigactonine (41), olivimine (43), and eserine in varying degrees. Their antifeedant or insecticidal potencies did not parallel their reported nAChR binding activity, but did correlate with the agonist/antagonist insecticidal/antifeedant model proposed for nicotininc insecticides. A few compounds [14, tuguaconitine (38), 14-demethyldelboxine (40), 19, dehydrodelsoline (36), 18-O-demethylpubescenine (13), 41, 9, and delcosine (23)] had selective cytotoxic effects to ward insect-derived Sf9 cells. None were cytotoxic to mammalian CHO cells and none increased Trypanosoma cruzi mortality. The selective cytotoxic effects of some structures indicate that they can act on biological targets other than neuroreceptors. 相似文献
87.
Cabeza MC Ordóñez JA Cambero I de la Hoz L García ML 《Journal of food protection》2004,67(9):1886-1891
The combined effects of simultaneous application of ultrasonic waves and heat treatment (thermoultrasonication) on the survival of a strain of Salmonella enterica Enteritidis was studied in both distilled water and intentionally contaminated intact eggs immersed in water. Although minor differences were observed between parameters obtained for thermoultrasonic treatment of bacteria suspended in water and those attached to the shell egg, the thermoultrasonication effects were considered to be of the same level in the range of temperatures assayed (52 to 58 degrees C). This combined process presented a clearly higher killing effect than the heat treatment alone. It decreased the decimal reduction times (D-values) by 80 to 55%, respectively, in the range of temperatures for heat treatment when the organism was suspended in water, which means a 99.5% reduction (5D to >2D) of the original bacterial load versus a 90% reduction for the heat treatment alone. The practical implications of the phenomenon are discussed. 相似文献
88.
Cellular localization and changes in expression of prolactin receptor isoforms in sheep ovary throughout the estrous cycle 总被引:3,自引:0,他引:3
Picazo RA García Ruiz JP Santiago Moreno J González de Bulnes A Muñoz J Silván G Lorenzo PL Illera JC 《Reproduction (Cambridge, England)》2004,128(5):545-553
The actions of prolactin (PRL) on target cells depend on the type of prolactin receptor (PRLr) predominantly expressed, particularly whether the long PRLr isoform is expressed. The aims of this study were to determine the cellular localization and the changes in expression of long and short PRLr isoforms in sheep ovary throughout the estrous cycle. Long and short PRLrs were localized mostly in the same ovarian cells. Maximum signal intensity, particularly for long PRLrs, was found in stromal cells surrounding primordial and primary follicles, and, for both PRLrs, in granulosa cells of preantral follicles and in luteal cells. Moderate signal intensity for PRLrs was found in theca cells of preantral to ovulatory follicles, and in granulosa cells of antral follicles up to the gonadotropin-dependent stage. Decreasing immunoreactivity to PRLrs was found in granulosa cells of gonadotropin-dependent to ovulatory follicles. For long PRLrs in particular, no signal was found in mural granulosa cells of gonadotropin-dependent follicles; for both isoforms, no signal was found in most granulosa cells of ovulatory follicles. In primordial to gonadotropin-dependent follicles, cellular localization of PRLr was similar on days 0, 10 and 15 of the cycle. Oocytes consistently showed positive immunostaining for PRLrs. Comparative RT-PCR analysis of long and short PRLr expression showed that the short isoform is evenly expressed throughout the estrous cycle, whereas the expression of the long form increases at the time of estrus and decreases at mid-luteal phase and at the onset of the follicular phase. Expression of long PRLrs was greater than that of short PRLrs on day 0 of cycle; expression of both isoforms was similar on day 10 and on day 15, long PRLrs expression was lower than that of short PRLrs. Our results indicate that in sheep ovary, the maximum responsiveness to PRL might occur during the preovulatory phase of the estrous cycle. 相似文献
89.
Continuous mandibular distraction osteogenesis using superelastic shape memory alloy (SMA) 总被引:7,自引:0,他引:7
Idelsohn S Peña J Lacroix D Planell JA Gil FJ Arcas A 《Journal of materials science. Materials in medicine》2004,15(4):541-546
Distraction osteogenesis is a well-established method of endogenous tissue engineering. It is a biological process of bone neo-formation between segments subjected to tension. The concept of this study was to investigate the distraction osteogenesis with a device capable of creating a permanent and constant force during the whole process as if a very large number of small elongations were applied constantly. The mechanical testing of the device used to produce the constant force and the in vivo analysis of the bone growth after it was implanted in rabbits are presented on this work. The device consists of a NiTi coil spring, superelastic at body temperature, in order to have a stress plateau during the austenitic retransformation during the unloading. The in vivo analysis was made on six female rabbits of 12 months old. A segmental mandibulectomy at the horizontal arm of the mandible and a corticotomy at 5mm distant from the gap were made. Next, following a latency period of five days, the SMA springs were implanted to induce the bone neo-formation. The displacement at the unloading plateau shows that it is necessary to have longer springs or to use several (available commercially) in series in order to fulfil the requirements of a human distraction. The temperature variations induced changes in the spring force. However, when the temperature returns to 37 degrees C the distraction force recovers near the initial level and does so completely when the distraction process continues. For the in vivo study, all six rabbits successfully completed the distraction. The radiographies showed the gap as distraction advanced. A continuity in the newly formed bone with similar transversal and horizontal dimensions than the original bone can be observed on the histologies. In conclusion, the application of a constant force on distraction osteogenesis, using SMA springs, may be a successful alternative to the conventional gradual distraction. 相似文献
90.
Fernández-Breis JT Martínez-Béjar R Vivancos-Vicente PJ Valencia-García R García-Sánchez F 《IEEE transactions on nanobioscience》2004,3(3):164-171
Data organization has become a strategic target for biologists due to the increasing volume of genomic data available for them. For this purpose, we need a complete knowledge model for representing biological system. In this paper, we deal with both processes for the creation and integration of shareable, reusable domain models within biology, which is a critical issue. In particular, this work introduces a new cooperative development approach for biology ontologies. This approach is based on the integration of the ontologies supplied by different human experts. Two experiments in biological domains are presented and their results discussed. 相似文献