首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   294678篇
  免费   5865篇
  国内免费   868篇
电工技术   5382篇
综合类   365篇
化学工业   44057篇
金属工艺   10870篇
机械仪表   9267篇
建筑科学   7250篇
矿业工程   1150篇
能源动力   7113篇
轻工业   28346篇
水利工程   2875篇
石油天然气   4045篇
武器工业   73篇
无线电   36280篇
一般工业技术   56187篇
冶金工业   54347篇
原子能技术   5560篇
自动化技术   28244篇
  2021年   2935篇
  2020年   2264篇
  2019年   2918篇
  2018年   4903篇
  2017年   4871篇
  2016年   5133篇
  2015年   3432篇
  2014年   5359篇
  2013年   14068篇
  2012年   8621篇
  2011年   10782篇
  2010年   8544篇
  2009年   9259篇
  2008年   10058篇
  2007年   9937篇
  2006年   8691篇
  2005年   7923篇
  2004年   7607篇
  2003年   7387篇
  2002年   7014篇
  2001年   6911篇
  2000年   6602篇
  1999年   6710篇
  1998年   16526篇
  1997年   11828篇
  1996年   9102篇
  1995年   7051篇
  1994年   6199篇
  1993年   6134篇
  1992年   4789篇
  1991年   4436篇
  1990年   4214篇
  1989年   3946篇
  1988年   3802篇
  1987年   3323篇
  1986年   3187篇
  1985年   3764篇
  1984年   3513篇
  1983年   3137篇
  1982年   2996篇
  1981年   3113篇
  1980年   2920篇
  1979年   2739篇
  1978年   2596篇
  1977年   3225篇
  1976年   4185篇
  1975年   2386篇
  1974年   2370篇
  1973年   2386篇
  1972年   1884篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
Lund  Brady D.  Maurya  Sanjay Kumar 《Scientometrics》2020,125(3):2491-2504
Scientometrics - This study investigates a potential relationship between highly-cited scholarly papers and the number of citations received by other papers with which they share a journal issue....  相似文献   
82.
Morozov  Yu. D.  Pemov  I. F.  Matrosov  M. Yu.  Zin’ko  B. F. 《Metallurgist》2020,63(9-10):933-950
Metallurgist - We consider domestic and foreign standards for rolled metals used in bridge building. Domestic standards contain elevated requirements to the reliability of rolled metals in terms of...  相似文献   
83.
Russian Journal of Non-Ferrous Metals - This article is devoted to the influence of sodium lignosulfonate (SL), anionic surfactants (sodium dodecylsulfate (SDS), sodium dodecylbenzene sulfonate...  相似文献   
84.
ABSTRACT

In this paper, we review some algebraic control system. Precisely, linear and bilinear systems on Euclidean spaces and invariant and linear systems on Lie groups. The fourth classes of systems have a common issue: to any class, there exists an associated subgroup. From this object, we survey the controllability property. Especially, from those coming from our contribution to the theory.  相似文献   
85.
The family of NAD(P)H-dependent short-chain dehydrogenases/reductases (SDRs) comprises numerous biocatalysts capable of C=O or C=C reduction. The highly homologous noroxomaritidine reductase (NR) from Narcissus sp. aff. pseudonarcissus and Zt_SDR from Zephyranthes treatiae, however, are SDRs with an extended imine substrate scope. Comparison with a similar SDR from Asparagus officinalis (Ao_SDR) exhibiting keto-reducing activity, yet negligible imine-reducing capability, and mining the Short-Chain Dehydrogenase/Reductase Engineering Database indicated that NR and Zt_SDR possess a unique active-site composition among SDRs. Adapting the active site of Ao_SDR accordingly improved its imine-reducing capability. By applying the same strategy, an unrelated SDR from Methylobacterium sp. 77 (M77_SDR) with distinct keto-reducing activity was engineered into a promiscuous enzyme with imine-reducing activity, thereby confirming that the ability to reduce imines can be rationally introduced into members of the “classical” SDR enzyme family. Thus, members of the SDR family could be a promising starting point for protein approaches to generate new imine-reducing enzymes.  相似文献   
86.
87.
Context: The administration of pharmabiotics is a promising alternative to antimicrobial drugs for the treatment and/or prevention of female urogenital infections.

Objective: To design pharmabiotic formulations including bioactive ingredients of microbial origin combined with non-microbial substances and then to evaluate the stability of the combinations during freeze-drying and storage.

Materials and methods: Different formulations including Lactobacillus gasseri CRL 1263, Lactobacillus salivarius CRL 1328, salivaricin CRL 1328 (a bacteriocin) and non-microbial compounds (lactose, inulin and ascorbic acid) were assayed, and the ingredients were freeze-dried together or separately. The formulations were stored in gelatin capsules at 4?°C for 360?d.

Results: The viability of lactobacilli was affected to different extents depending on the strains and on the formulations assayed. L. salivarius and ascorbic acid were successfully combined only after the freeze-drying process. Salivaricin activity was not detected in formulations containing L. gasseri. However, when combined with ascorbic acid, lactose, inulin or L. salivarius, the bacteriocin maintained its activity for 360?d. The selected microorganisms proved to be compatible for their inclusion in multi-strain formulations together with lactose, inulin and ascorbic acid. Salivaricin could be included only in a L. salivarius CRL 1328 single-strain formulation together with non-microbial substances.

Conclusions: This study provides new insights into the design of urogenital pharmabiotics combining beneficial lactobacilli, salivaricin CRL 1328 and compounds with different functionalities.  相似文献   
88.
89.
An alternative Equivalent Electrical Circuit for Proton Exchange Membrane Fuel Cells is modelled in this study. Both I–V characteristics and H2 consumptions corresponding to generated power under load and no-load conditions are investigated. For this purpose, H2 consumptions and I–V characteristics of three different sized PEMFCs are tested. There is a very good harmony between the model results and measured values (relative error %0.7, %6.4 and %2.5 for FC-A, FC-B and FC-C respectively). In the proposed model current passes only on parallel resistance and not on serial resistance at no-load condition. Thus, a FC with higher parallel resistance should be preferred. Another key output of this study is that based on the proposed model, performance comparison of FCs can be performed with the parameters defined in this work. Proposals made in this study can easily be used for performance analysis of FCs under for both steady state and transient analysis.  相似文献   
90.
Powder Metallurgy and Metal Ceramics - The theoretical strength of LaB6 and MeB2 borides and a eutectic LaB6–TiB2 system is calculated with quasiharmonic approximation for uniaxial strain in...  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号