全文获取类型
收费全文 | 4457篇 |
免费 | 173篇 |
国内免费 | 20篇 |
专业分类
电工技术 | 293篇 |
综合类 | 14篇 |
化学工业 | 1344篇 |
金属工艺 | 160篇 |
机械仪表 | 132篇 |
建筑科学 | 125篇 |
矿业工程 | 5篇 |
能源动力 | 217篇 |
轻工业 | 413篇 |
水利工程 | 18篇 |
石油天然气 | 6篇 |
无线电 | 330篇 |
一般工业技术 | 917篇 |
冶金工业 | 144篇 |
原子能技术 | 131篇 |
自动化技术 | 401篇 |
出版年
2023年 | 30篇 |
2021年 | 124篇 |
2020年 | 60篇 |
2019年 | 73篇 |
2018年 | 86篇 |
2017年 | 69篇 |
2016年 | 112篇 |
2015年 | 84篇 |
2014年 | 125篇 |
2013年 | 270篇 |
2012年 | 257篇 |
2011年 | 297篇 |
2010年 | 247篇 |
2009年 | 262篇 |
2008年 | 289篇 |
2007年 | 225篇 |
2006年 | 218篇 |
2005年 | 145篇 |
2004年 | 151篇 |
2003年 | 170篇 |
2002年 | 152篇 |
2001年 | 82篇 |
2000年 | 82篇 |
1999年 | 66篇 |
1998年 | 93篇 |
1997年 | 67篇 |
1996年 | 68篇 |
1995年 | 60篇 |
1994年 | 56篇 |
1993年 | 60篇 |
1992年 | 55篇 |
1991年 | 58篇 |
1990年 | 42篇 |
1989年 | 49篇 |
1988年 | 18篇 |
1987年 | 39篇 |
1986年 | 24篇 |
1985年 | 39篇 |
1984年 | 21篇 |
1983年 | 34篇 |
1982年 | 32篇 |
1981年 | 28篇 |
1980年 | 18篇 |
1979年 | 22篇 |
1978年 | 23篇 |
1977年 | 16篇 |
1976年 | 10篇 |
1975年 | 10篇 |
1974年 | 8篇 |
1973年 | 7篇 |
排序方式: 共有4650条查询结果,搜索用时 187 毫秒
991.
In diabetic peripheral neuropathy (DPN), metabolic disorder by hyperglycemia progresses in peripheral nerves. In addition to the direct damage to peripheral neural axons, the homeostatic mechanism of peripheral nerves is disrupted by dysfunction of the blood–nerve barrier (BNB) and Schwann cells. The disruption of the BNB, which is a crucial factor in DPN development and exacerbation, causes axonal degeneration via various pathways. Although many reports revealed that hyperglycemia and other important factors, such as dyslipidemia-induced dysfunction of Schwann cells, contributed to DPN, the molecular mechanisms underlying BNB disruption have not been sufficiently elucidated, mainly because of the lack of in vitro studies owing to difficulties in establishing human cell lines from vascular endothelial cells and pericytes that form the BNB. We have developed, for the first time, temperature-sensitive immortalized cell lines of vascular endothelial cells and pericytes originating from the BNB of human sciatic nerves, and we have elucidated the disruption to the BNB mainly in response to advanced glycation end products in DPN. Recently, we succeeded in developing an in vitro BNB model to reflect the anatomical characteristics of the BNB using cell sheet engineering, and we established immortalized cell lines originating from the human BNB. In this article, we review the pathologic evidence of the pathology of DPN in terms of BNB disruption, and we introduce the current in vitro BNB models. 相似文献
992.
The orthogonal segment intersection search problem is stated as follows: given a setS ofn orthogonal segments in the plane, report all the segments ofS that intersect a given orthogonal query segment. For this problem, we propose a simple and practical algorithm based on bucketing techniques. It constructs, inO(n) time preprocessing, a search structure of sizeO(n) so that all the segments ofS intersecting a query segment can be reported inO(k) time in the average case, wherek is the number of the reported segments. The proposed algorithm as well as existing algorithms is implemented in FORTRAN, and their practical efficiencies are investigated through computational experiments. It is shown that ourO(k) search time,O(n) space, andO(n) preprocessing time algorithm is in practice the most efficient among the algorithms tested. 相似文献
993.
Akira Nakajima Takashi Sakaguchi 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》1993,57(4):321-326
Some attempts were made to recover gold from aqueous systems using immobilized persimmon tannin. This adsorbent adsorbed gold from solutions containing hydrogen tetrachloroaurate(III) with high efficiency, whereas there was minimal adsorption from solutions containing gold(I) sodium thiomalate and sodium dicyanoaurate(I). The adsorption of gold was rapid, and was affected by the pH of the solution, temperature, external gold concentration and amount of adsorbent. Adsorbed gold was easily desorbed with 1 mol dm?3 thiourea solution, indicating that immobilized persimmon tannin can be repeatedly re-used for the recovery of gold using adsorption-desorption cycles. 相似文献
994.
995.
Tadashi Fukami Takashi Ishizaka Toshio Miyamoto 《Electrical Engineering in Japan》1996,117(3):110-121
A synchronous-induction motor, with the features of both a synchronous motor and a wound-rotor induction motor, far excels other synchronous motors in starting characteristics. However, a major drawback of the synchronous-induction motor is the need for an excitation power supply with low-voltage, large-current power rating. For this reason, its driving equipment becomes large, and increases overall cost. This paper proposes a new synchronous-induction motor, absent the problems involved in making the motor a self-excited type. It employs the second-space harmonic component of armature reaction field to obtain the self-excitation of the field system, and installs a harmonic winding, which is used for extraction of an excitation power, in the rotor. This new self-excited motor has the following advantages: (1) the driving equipment is small, since no excitation power supply is involved; and (2) due to the effect of the series characteristic by which the field current varies in proportion to the load current automatically, the motor can be operated with a good power factor. In the present paper the structure and operating principle of the new motor are explained and the basic characteristics are also investigated by means of a simple analysis and experimental results with a 1.5-kV trial machine. 相似文献
996.
Kazuhiro Kajikawa Katsuyuki Kaiho Mitsuyoshi Yamamoto Hiroshi Fuji Nobuyuki Sadakata Takashi Saito Osamu Kohno 《Electrical Engineering in Japan》1996,117(5):34-43
Recently, multifilamentary superconducting wires with very low ac losses have been produced and practical applications will now be considered. To realize actualsize power machines and apparatuses, it is necessary to develop 1 - 10 kA ac conductors. However, the critical currents of multifilamentary wires at 1 T are several tens of A, and therefore it is necessary to use multistrand conductors consisting of several tens or several hundreds of strands. Such conductors sometimes show ac current degradation because of such factors as (1) nonuniform current distribution, (2) wire motion, (3) temperature increase, (4) longitudinal magnetic field effect, etc. Formerly, a coreless transformer was considered unpractical because of its large exciting current. However, Yamamoto and others proposed that a coreless superconducting transformer could be used as a stepdown autotransformer at the receiving side, utilizing its large exciting current as the reactive power source to cancel the charging current of an underground transmission line or UHV line, and therefore the shunt reactors could be eliminated. In this paper, development of ac-superconducting conductors aimed at prevention of current degradation are discussed, as well as quench test results of two small coils made with these conductors. In these conductors, low ac low strands with ultrafine NbTi filaments are twisted around a central bundle of stainless steel wires. One of the coils has been designed as a model coreless autotransformer, and its test result is also described. 相似文献
997.
J E Stein W L Reichert M Nishimoto U Varanasi 《The Science of the total environment》1990,94(1-2):51-69
The levels of aromatic hydrocarbons in sediments of Puget Sound, Washington, are positively correlated with the prevalence of hepatic neoplasms and related lesions in English sole (Parophrys vetulus). To investigate the biochemical processes involved in chemical carcinogenesis in fish from Puget Sound, we have studied the uptake, activation, and detoxication of polycyclic aromatic hydrocarbons (PAHs) in English sole, and have compared these data to PAH metabolism in a related species, starry flounder (Platichthys stellatus), which shows a lower prevalence of hepatic neoplasms than sole. The results of both laboratory and field studies show that sediment-associated PAHs are biologically available to both flatfish species, and that both species accumulate similar levels of PAHs. Analyses of hepatic DNA from sole using the 32P-postlabeling technique indicate that xenobiotic chemicals were adducted to hepatic DNA of fish from the contaminated sites but not to the DNA of fish from reference sites. Studies of the ability of English sole and starry flounder to metabolize benzo(a)pyrene (BaP) and bind reactive BaP intermediates to hepatic DNA indicate that biochemical differences in the metabolism of carcinogenic PAHs may explain, at least in part, the apparent lower susceptibility of starry flounder than English sole to chemically induced hepatocarcinogenesis. 相似文献
998.
Hisayoshi Mitamura Seiichiro Matsumoto Takashi Miyazaki Timothy J. White Kiyoshi Nukaga Yoshihiro Togashi Tamio Sagawa Shingo Tashiro Desmond M. Levins Akira Kikuchi 《Journal of the American Ceramic Society》1990,73(11):3433-3441
The polyphase titanate ceramic containing sodium-rich simulated high-level nuclear waste was doped with 0.69 wt% of 244 Cm to accelerate long-term self-irradiation due to α decays. α autoradiography showed that α emissions were almost uniformaly distributed throughout the curium-doped samples on a >20-μm scale although micropore surfaces and titanium oxide agglomerates were free of α-emitting nuclides. The phase assemblage of the curium-doped titanate ceramic included freudenbergite and loveringite in addition to the more abundant oxide phases: hollandite, perovskite, and zirconolite. Accumulation of α decays was accompanied by a gradual decrease in density. The increment of density was – 1% after an equivalent age of 5000 yr. Leach tests showed a slight trend toward higher total release of curium with equivalent age. The release of soluble nonradioactive elements (e.g., Na, Cs, Sr, and Ca) in the oldest specimens (equivalent age, 2000 yr) varied from specimen to specimen but, on average, were higher than specimens that had suffered a lower radiation dose. 相似文献
999.
The flexural vibration analysis of rectangular Mindlin plates using the collocation method is described. The results obtained by the present method are compared with published results for plates with uniform thickness and two opposite edges simply supported. The comparison shows that the method yields very good results with a relatively small number of collocation points, and that estimates for the higher modes can be obtained without any difficulties. Furthermore, the method is applied to plates with linearly varying thickness, and new findings are presented for the frequencies of plates. 相似文献
1000.