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   316281篇
  免费   5775篇
  国内免费   1407篇
电工技术   5372篇
综合类   799篇
化学工业   47088篇
金属工艺   12156篇
机械仪表   9241篇
建筑科学   7975篇
矿业工程   1777篇
能源动力   8011篇
轻工业   27951篇
水利工程   3345篇
石油天然气   5932篇
武器工业   49篇
无线电   36205篇
一般工业技术   64151篇
冶金工业   56732篇
原子能技术   7794篇
自动化技术   28885篇
  2021年   3211篇
  2020年   2450篇
  2019年   2909篇
  2018年   4815篇
  2017年   4950篇
  2016年   5213篇
  2015年   3558篇
  2014年   5804篇
  2013年   14592篇
  2012年   8947篇
  2011年   12060篇
  2010年   9347篇
  2009年   10551篇
  2008年   10872篇
  2007年   10765篇
  2006年   9067篇
  2005年   8414篇
  2004年   8342篇
  2003年   8061篇
  2002年   7804篇
  2001年   7760篇
  2000年   7163篇
  1999年   7394篇
  1998年   18188篇
  1997年   12831篇
  1996年   9478篇
  1995年   7460篇
  1994年   6508篇
  1993年   6539篇
  1992年   4617篇
  1991年   4466篇
  1990年   4317篇
  1989年   4227篇
  1988年   3949篇
  1987年   3538篇
  1986年   3544篇
  1985年   3975篇
  1984年   3676篇
  1983年   3346篇
  1982年   3200篇
  1981年   3225篇
  1980年   3184篇
  1979年   2949篇
  1978年   2984篇
  1977年   3306篇
  1976年   4372篇
  1975年   2540篇
  1974年   2456篇
  1973年   2477篇
  1972年   2073篇
排序方式: 共有10000条查询结果,搜索用时 953 毫秒
1.
2.
Wireless Personal Communications - Chronic kidney disease (CKD) is a gradual loss of kidney function over the period of time and it is irrevocable once functionality reaches the critical state....  相似文献   
3.
Transmission electron microscopy (TEM) is an important analysis technique to visualize (bio)macromolecules and their assemblies, including collagen fibers. Many protocols for TEM sample preparation of collagen involve one or more washing steps to remove excess salts from the dispersion that could hamper analysis when dried on a TEM grid. Such protocols are not standardized and washing times as well as washing solvents vary from procedure to procedure, with each research group typically having their own protocol. Here, we investigate the influence of washing with water, ethanol, but also methanol and 2-propanol, for both mineralized and unmineralized collagen samples via a protocol based on centrifugation. Washing with water maintains the hydrated collagen structure and the characteristic banding pattern can be clearly observed. Conversely, washing with ethanol results in dehydration of the fibrils, often leading to aggregation of the fibers and a less obvious banding pattern, already within 1 min of ethanol exposure. As we show, this process is fully reversible. Similar observations were made for methanol and propanol. Based on these results, a standardized washing protocol for collagenous samples is proposed.  相似文献   
4.
Food Science and Biotechnology - A rich source of nutrients, figs have a number of clinically validated benefits. This study aimed to evaluate the in vitro simulated gastrointestinal digestion, and...  相似文献   
5.
Multimedia Tools and Applications - In this work, a new fuzzy logic-based algorithm is proposed for the enhancement of low light color images. A generalization of a fuzzy set known as an...  相似文献   
6.
Multimedia Tools and Applications - Endometriosis is a common gynecologic condition typically treated via laparoscopic surgery. Its visual versatility makes it hard to identify for non-specialized...  相似文献   
7.
Forschung im Ingenieurwesen - Das Arbeitsmittel in Wärmepumpen unterliegt einer Vielzahl von Anforderungen, welche für einen effizienten und sicheren Betrieb eingehalten werden...  相似文献   
8.

We discuss the temperature dependence of a common low temperature local thermometer, a tunnel junction between a superconductor and a normal metal (NIS junction). Towards the lowest temperatures its characteristics tend to saturate, which is usually attributed to selfheating effects. In this technical note, we reanalyze this saturation and show that the temperature independent subgap current of the junction alone explains in some cases the low temperature behavior quantitatively.

  相似文献   
9.
Journal of Chemical Ecology - Biocontrol agents such as parasitic wasps use long-range volatiles and host-associated cues from lower trophic levels to find their hosts. However, this chemical...  相似文献   
10.
A set of novel hydrazone derivatives were synthesized and analyzed for their biological activities. The compounds were tested for their inhibitory effect on the phosphorylating activity of the protein kinase CK2, and their antioxidant activity was also determined in three commonly used assays. The hydrazones were evaluated for their radical scavenging against the DPPH, ABTS and peroxyl radicals. Several compounds have been identified as good antioxidants as well as potent protein kinase CK2 inhibitors. Most hydrazones containing a 4-N(CH3)2 residue or perfluorinated phenyl rings showed high activity in the radical-scavenging assays and possess nanomolar IC50 values in the kinase assays.  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