全文获取类型
收费全文 | 3439篇 |
免费 | 63篇 |
国内免费 | 5篇 |
专业分类
电工技术 | 13篇 |
化学工业 | 163篇 |
金属工艺 | 14篇 |
机械仪表 | 15篇 |
建筑科学 | 13篇 |
能源动力 | 20篇 |
轻工业 | 199篇 |
水利工程 | 5篇 |
石油天然气 | 9篇 |
无线电 | 69篇 |
一般工业技术 | 109篇 |
冶金工业 | 2801篇 |
原子能技术 | 3篇 |
自动化技术 | 74篇 |
出版年
2023年 | 8篇 |
2022年 | 2篇 |
2021年 | 13篇 |
2020年 | 16篇 |
2019年 | 25篇 |
2018年 | 19篇 |
2017年 | 23篇 |
2016年 | 32篇 |
2015年 | 22篇 |
2014年 | 40篇 |
2013年 | 54篇 |
2012年 | 47篇 |
2011年 | 43篇 |
2010年 | 35篇 |
2009年 | 35篇 |
2008年 | 34篇 |
2007年 | 40篇 |
2006年 | 36篇 |
2005年 | 19篇 |
2004年 | 27篇 |
2003年 | 18篇 |
2002年 | 19篇 |
2001年 | 23篇 |
2000年 | 14篇 |
1999年 | 89篇 |
1998年 | 949篇 |
1997年 | 541篇 |
1996年 | 275篇 |
1995年 | 176篇 |
1994年 | 161篇 |
1993年 | 176篇 |
1992年 | 21篇 |
1991年 | 23篇 |
1990年 | 23篇 |
1989年 | 41篇 |
1988年 | 35篇 |
1987年 | 23篇 |
1986年 | 22篇 |
1985年 | 25篇 |
1983年 | 7篇 |
1982年 | 13篇 |
1981年 | 17篇 |
1980年 | 23篇 |
1979年 | 2篇 |
1978年 | 6篇 |
1977年 | 58篇 |
1976年 | 150篇 |
1975年 | 2篇 |
1955年 | 2篇 |
1954年 | 1篇 |
排序方式: 共有3507条查询结果,搜索用时 62 毫秒
91.
92.
MR Kirshenbaum SF Chen CH Behrens LM Papp MM Stafford JH Sun DL Behrens JR Fredericks ST Polkus P Sipple 《Canadian Metallurgical Quarterly》1994,54(8):2199-2206
(R,R)-2,2'-[1,2-ethanediylbis[imino(1-methyl-2,1-ethanediyl)]]- bis[5-nitro-1H-benz[de]isoquinoline-1,3-(2H)-dione] dimethanesulfonate (DMP 840), is a bis-naphthalimide anticancer tumoricidal agent currently in phase I clinical trials. DMP 840 exhibits curative activity in human tumor xenografts, where it shows selectivity for human solid tumors over murine leukemias. In contrast to the selectivity found for DMP 840 in vivo, DMP 840 exhibits potent antiproliferative activity in vitro against a variety of human and murine leukemia and solid tumor cell lines in culture, with inhibitory doses that reduce the number of treated cells to one half (IC50) values ranging from 2.3 to 53 nM. DMP 840 was growth inhibitory to three doxorubicin-resistant cell lines with IC50 values also in the nanomolar range. Clonogenic survival experiments showed that DMP 840 was equally cytotoxic to both exponentially growing and quiescent human clone A colon carcinoma cells. A 1-h incubation of DMP 840 (1.22-12 microM) caused 5-log cell kill in KB-3-1 human epidermoid carcinoma, clone A human colon carcinoma, and L1210 murine leukemia cell lines. The rapid cell killing by DMP 840 in clonogenic survival experiments and initial mechanism of action studies was consistent with a DNA-interactive mechanism for DMP 840 cytotoxicity. Mechanism of action studies in L1210 leukemia cells demonstrated that DMP 840 inhibited the incorporation of thymidine and uridine into DNA and RNA with IC50 values of 0.55 and 0.08 microM, respectively. DMP 840 produced DNA single-strand breaks in a dose-dependent manner. Double-strand breaks were not observed with DMP 840 treatment, even at higher concentrations of compound. Chinese hamster ovary (CHO) and P388 cells resistant to camptothecin and containing a mutant form of topoisomerase I were also used to evaluate whether DMP 840 was cross-resistant with agents active against topoisomerase I. While the CHOR line was 163-fold resistant to camptothecin, the CHOR line was only 1.7-fold resistant to DMP 840. In summary, DMP 840 is a DNA-interactive agent that demonstrates excellent antiproliferative activity in vitro against cultured tumor cells from both human and murine sources. Its mechanism of tumoricidal activity may be novel. 相似文献
93.
94.
Raffaele Sacchi Isabel Medina Santiago P. Aubourg Francesco Addeo Livio Paolillo 《Journal of the American Oil Chemists' Society》1993,70(3):225-228
Based on proton nuclear magnetic resonance (1H-NMR) spectroscopy, a rapid and structure-specific method for the determination of ω-3 polyunsaturated fatty acids (PUFAs)
in fish lipids is presented. The different chemical shift observed for the methyl resonance of ω-3 PUFAs (δ=0.95 ppm) with
respect to the methyl resonance of all other fatty acids (δ=0.86 ppm) has provided the possibility of proposing a new and
rapid method for the determination of ω-3 PUFA content. Twenty-four fish lipid samples (raw, cooked and canned albacore tuna)
produced results that showed good agreement between1H-NMR analysis and gas chromatographic determination. Raw and cooked samples showed significantly higher levels of ω-3 PUFA
than canned tuna. 相似文献
95.
The design of industrial distillation columns is normally based on estimated values of plate efficiencies. Several different plate efficiency models have been proposed in the literature and among them the one presented by Murphree is widely used in spite of its limitations. However the difficulties involved in the use of Murphree's model are not present if Hausen's model is considered.In the present paper a comparative study of the two models considering both binary and multicomponent systems is presented. A graphical relationship beExperimental composition profiles obtained in small laboratory columns with binary and ternary systems are interpreted in terms of Hausen efficiencies.It is argued that the use of the Hausen efficiency model should be wider as it overcomes limitations of Murphree's model and is in agreement with physi 相似文献
96.
Jonghyun Oh Kewei Liu Tim Medina Francis Kralick Hongseok Noh 《Microsystem Technologies》2014,20(6):1169-1179
We present a microfabricated 10 by 10 array of microneedles for the treatment of a neurological disease called communicating hydrocephalus. Together with the previously reported microvalve array, the current implantable microneedle array completes the microfabricated arachnoid granulations (MAGs) that mimic the function of normal arachnoid granulations. The microneedle array was designed to enable the fixation of the MAGs through dura mater membrane in the brain and thus provide a conduit for the flow of cerebrospinal fluid. Cone-shaped microneedles with hollow channels were fabricated using a series of microfabrication techniques: SU-8 photolithography for tapered geometry, reactive ion etching for sharpening the microneedles, 248 nm deep UV excimer laser machining for creating through-hole inside the microneedles, and metal sputtering for improved rigidity. Puncture tests were conducted using porcine dura mater and the results showed that the fabricated microneedle array is strong enough to pierce the dura mater. The in vitro biocompatibility test result showed that none of the 100 outlets of the microneedles exposed to the bloodstream were clogged significantly by blood cells. We believe that these test results demonstrate the potential use of the microneedle array as a new treatment of hydrocephalus. 相似文献
97.
A. Robles Medina A. Giménez Giménez F. García Camacho J. A. Sánchez Pérez E. Molina Grima A. Contreras Gómez 《Journal of the American Oil Chemists' Society》1995,72(5):575-583
n-3 Polyunsaturated fatty acids (n-3 PUFA) from the marine microalgaIsochrysis galbana were concentrated and purified by a two-step process—formation of urea inclusion compounds followed by preparative high-performance
liquid chromatography. These methods had been developed previously with fatty acids from cod liver oil. By the urea inclusion
compounds method, a mixture that contained 94% (w/w) stearidonic (SA), eicosapentaenoic (EPA), plus docosahexaenoic (DHA)
acids (4:1 urea/fatty acid ratio and 4°C crystallization final temperature) was obtained from cod liver oil fatty acids. Further
purification of SA, EPA, and DHA was achieved with reverse-phase C18 columns. These isolations were scaled up to a semi-preparative column. A PUFA concentrate was isolated fromI. galbana with methanol/water (80:20, w/w) or ethanol/water (70:30, w/w). With methanol/water, a 96% EPA fraction with 100% yield was
obtained, as well as a 94% pure DHA fraction with a 94% yield. With ethanol/water as the mobile phase, EPA and DHA fractions
obtained were 92% pure with yields of 84 and 88%, respectively. 相似文献
98.
M. Cartens E. Molina Grima A. Robles Medina A. Giménez Giménez J. Ibáñez González 《Journal of the American Oil Chemists' Society》1996,73(8):1025-1031
Eicosapentaenoic acid (EPA, 20∶5n-3) was obtained from the marine microalgaePhaeodactylum tricornutum by a three-step process: fatty acid extraction by direct saponification of biomass, polyunsaturated fatty acid (PUFA) concentration
by formation of urea inclusion compounds, and EPA isolation by semipreparative high-performance liquid chromatography (HPLC).
Alternatively, EPA was obtained by a similar two-step process without the PUFA concentration step by the urea method. Direct
saponification of biomass was carried out with two solvents that contained KOH for lipid saponification. An increase in yield
was obtained because the problems associated with emulsion formation were avoided by separating the biomass from the soap
solution before adding hexane for extraction of insaponifiables. The most efficient solvent, ethanol (96%) at 60°C for 1 h,
extracted 98.3% of EPA. PUFA were concentrated by the urea method with a urea/fatty acid ratio of 4∶1 at a crystallization
temperature of 28°C and by using methanol and ethanol as urea solvents. An EPA concentration ratio of 1.73 (55.2∶31.9) and
a recover yield of 78.6% were obtained with methanol as the urea solvent. This PUFA concentrate was used to obtain 93.4% pure
EPA by semipreparative HPLC with a reverse-phase, C18, 10 mm i.d.×25-cm column and methanol/water (1% acetic acid), 80∶20 w/w, as the mobile phase. Eighty-five percent of EPA
loaded was recovered, and 65.7% of EPA present inP. tricornutum biomass was recovered in highly pure form by this three-step downstream process. Alternatively, 93.6% pure EPA was isolated
from the fatty acid extract (without the PUFA concentration step) with 100% EPA recovery yield. This two-step process increases
the overall EPA yield to 98.3%, but it is only possible to obtain 20% as much EPA as that obtained by three-step downstream
processing. 相似文献
99.
A comparative study of the phospholipids of white muscle of six of the comercially utilized tuna species, including quantitative
analyses of phospholipid classes and studies of the acyl composition of the major components. Plasmalogen compounds also were
identified and quantified. Choline and ethanolamine glycerophospholipids were the most abundant classes in all the samples,
as well as the only molecules containing plasmalogens (16∶0, 18∶0, and 18∶1 alkenyl ether chains). The patterns of fatty acid
distribution within each of the phospholipid classes showed general similarities in the species analyzed. However, ratios
between certain saturated and polyunsaturated fatty acids in different phospholipid classes showed remarkable diffences. The
high content of n−3 polyunsaturated fatty acids in the principal phospholipids, such as the plasmalogens, and taking into
account the fatty acids possible importance in human nutrition, indicates that the white muscle of tuna species may be a potentially
important dietary item. 相似文献
100.
S. Abell F. Medina D. Tichit J. Prez-Ramírez J.E. Sueiras P. Salagre Y. Cesteros 《Applied catalysis. B, Environmental》2007,70(1-4):577-584
In this paper, activated Mg-Al hydrotalcites were used as catalysts in the aldol condensation of campholenic aldehyde and methyl ethyl ketone (MEK). These materials represent an attractive alternative to less environmentally friendly liquid bases in a number of base-catalyzed reactions involved in the pharmaceutical and fragrance industries. The presence of basic hydroxyl groups in the interlayer space leads to very active materials. However, the relation between the activity of reconstructed hydrotalcites and the rehydration procedure is still not well understood. Different rehydration protocols in combination with extensive characterization studies were performed, including XRD, SEM, IR spectroscopy and TPD of CH3CN and CH3NO2. The materials were tested as catalysts in the aldol condensation of campholenic aldehyde and MEK, and relationships between the catalytic performance of the activated hydrotalcites and the rehydration procedure were derived. Several factors may influence the activity and selectivity of this reaction, such as the reaction temperature, the molar ratio of the reactants and the degree of rehydration of the hydrotalcite-like catalysts. The selectivity towards the formation of the desired branched isomer increases when performing the reaction at low temperatures. 相似文献