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   278048篇
  免费   7147篇
  国内免费   690篇
电工技术   4074篇
综合类   197篇
化学工业   44821篇
金属工艺   9500篇
机械仪表   7582篇
建筑科学   7312篇
矿业工程   1461篇
能源动力   6909篇
轻工业   28936篇
水利工程   3030篇
石油天然气   4365篇
武器工业   14篇
无线电   26854篇
一般工业技术   53452篇
冶金工业   54615篇
原子能技术   5441篇
自动化技术   27322篇
  2022年   2005篇
  2021年   3556篇
  2020年   2681篇
  2019年   3204篇
  2018年   5545篇
  2017年   5542篇
  2016年   5850篇
  2015年   4020篇
  2014年   5945篇
  2013年   14729篇
  2012年   9632篇
  2011年   11474篇
  2010年   9169篇
  2009年   9604篇
  2008年   9848篇
  2007年   9561篇
  2006年   7872篇
  2005年   7171篇
  2004年   6725篇
  2003年   6448篇
  2002年   5986篇
  2001年   5687篇
  2000年   5546篇
  1999年   5865篇
  1998年   16792篇
  1997年   11578篇
  1996年   8684篇
  1995年   6041篇
  1994年   5384篇
  1993年   5214篇
  1992年   3632篇
  1991年   3488篇
  1990年   3268篇
  1989年   3323篇
  1988年   3189篇
  1987年   2716篇
  1986年   2629篇
  1985年   3061篇
  1984年   2814篇
  1983年   2570篇
  1982年   2378篇
  1981年   2515篇
  1980年   2339篇
  1979年   2328篇
  1978年   2312篇
  1977年   2840篇
  1976年   4172篇
  1975年   1977篇
  1974年   1887篇
  1973年   1934篇
排序方式: 共有10000条查询结果,搜索用时 109 毫秒
91.
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   
92.
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   
93.
The enhancement of the thermal conductivity, keeping the electrical insulation, of epoxy thermosets through the addition of pristine and oxidized carbon nanotubes (CNTs) and microplatelets of boron nitride (BN) was studied. Two different epoxy resins were selected: a cycloaliphatic (ECC) epoxy resin and a glycidylic (DGEBA) epoxy resin. The characteristics of the composites prepared were evaluated and compared in terms of thermal, thermomechanical, rheological and electrical properties. Two different dispersion methods were used in the addition of pristine and oxidized CNTs depending on the type of epoxy resin used. Slight changes in the kinetics of the curing reaction were observed in the presence of the fillers. The addition of pristine CNTs led to a greater enhancement of the mechanical properties of the ECC composite whereas the oxidized CNTs presented a greater effect in the DGEBA matrix. The addition of CNTs alone led to a marked decrease of the electrical resistivity of the composites. Nevertheless, in the presence of BN, which is an electrically insulating material, it was possible to increase the proportion of pristine CNTs to 0.25 wt% in the formulation without deterioration of the electrical resistivity. A small but significant synergic effect was determined when both fillers were added together. Improvements of about 750% and 400% in thermal conductivity were obtained in comparison to the neat epoxy matrix for the ECC and DGEBA composites, respectively. © 2019 Society of Chemical Industry  相似文献   
94.
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   
95.
96.
97.
98.
99.
Potential mGAT4 inhibitors derived from the lead substance (S)-SNAP-5114 have been synthesized and characterized for their inhibitory potency. Variations from the parent compound included the substitution of one of its aromatic 4-methoxy and 4-methoxyphenyl groups, respectively, with a more polar moiety, including a carboxylic acid, alcohol, nitrile, carboxamide, sulfonamide, aldehyde or ketone function, or amino acid partial structures. Furthermore, it was investigated how the substitution of more than one of the aromatic 4-methoxy groups affects the potency and selectivity of the resulting compounds. Among the synthesized test substances (S)-1-{2-[(4-formylphenyl)bis(4-methoxyphenyl)-methoxy]ethyl}piperidine-3-carboxylic acid, that features a carbaldehyde function in place of one of the aromatic 4-methoxy moieties of (S)-SNAP-5114, was found to have a pIC50 value of 5.89±0.07, hence constituting a slightly more potent mGAT4 inhibitor than the parent substance while showing comparable subtype selectivity.  相似文献   
100.
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