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   989篇
  免费   3篇
  国内免费   1篇
化学工业   17篇
金属工艺   3篇
机械仪表   8篇
建筑科学   4篇
能源动力   2篇
轻工业   10篇
无线电   9篇
一般工业技术   19篇
冶金工业   902篇
自动化技术   19篇
  2021年   1篇
  2019年   1篇
  2018年   2篇
  2017年   1篇
  2016年   1篇
  2014年   1篇
  2013年   14篇
  2012年   1篇
  2011年   1篇
  2010年   1篇
  2009年   1篇
  2008年   1篇
  2007年   2篇
  2006年   3篇
  2005年   1篇
  2003年   2篇
  2002年   5篇
  2001年   7篇
  1999年   40篇
  1998年   304篇
  1997年   165篇
  1996年   99篇
  1995年   56篇
  1994年   48篇
  1993年   54篇
  1992年   3篇
  1991年   11篇
  1990年   10篇
  1989年   7篇
  1988年   12篇
  1987年   12篇
  1986年   3篇
  1985年   5篇
  1983年   7篇
  1982年   4篇
  1981年   9篇
  1980年   7篇
  1979年   2篇
  1977年   23篇
  1976年   53篇
  1975年   3篇
  1973年   1篇
  1972年   1篇
  1971年   1篇
  1968年   1篇
  1967年   1篇
  1964年   1篇
  1957年   2篇
  1955年   1篇
  1939年   1篇
排序方式: 共有993条查询结果,搜索用时 15 毫秒
1.
The bromodomain and extra terminal (BET) family of bromodomain-containing proteins (BCPs) have been the subject of extensive research over the past decade, resulting in a plethora of high-quality chemical probes for their tandem bromodomains. In turn, these chemical probes have helped reveal the profound biological role of the BET bromodomains and their role in disease, ultimately leading to a number of molecules in active clinical development. However, the BET subfamily represents just 8/61 of the known human bromodomains, and attention has now expanded to the biological role of the remaining 53 non-BET bromodomains. Rapid growth of this research area has been accompanied by a greater understanding of the requirements for an effective bromodomain chemical probe and has led to a number of new non-BET bromodomain chemical probes being developed. Advances since December 2015 are discussed, highlighting the strengths/caveats of each molecule, and the value they add toward validating the non-BET bromodomains as tractable therapeutic targets.  相似文献   
2.
本文对国内外卫星通信的最新发展作了详尽论述;并综合概括了未来卫星通信技术的发展趋势;最后,对卫星通信市场进行了预测。  相似文献   
3.
本文介绍低轨小卫星的发展和应用前景。低轨小卫星,体积和重量小,轨道低,功能单一,智能化,制造和发射都很容易,投资费用低,受到用户的普遍欢迎,有广阔的发展和应用前景。 小卫星在近几年发展迅速,应用广泛,已经受到世界各国的重视。在许多方面,已经应用小卫星和计划中应用小卫星的例子很多,本文只作简要介绍,目的在于引起人们的重视,发展我国的小卫星事业。  相似文献   
4.
Techniques which are currently used to measure skeletal muscle blood flow (SMBF) in patients with congestive heart failure (CHF) are neither convenient nor accurate. They have led to discrepant results in patients with congestive heart failure and are, in part, responsible for the ongoing debate regarding the factors which limit the rise in body oxygen consumption during exercise in these patients. However, direct measurement of SMBF may not be needed during exercise in patients with severe CHF. Their skeletal muscles maximally extract oxygen. Consequently, increase in oxygen consumption by the skeletal muscles is only mediated by a concomitant increase in SMBF. In patients with severe CHF, peak body oxygen consumption attained during maximal exercise closely depends on the rise in SMBF, and thus provides an indirect measurement of SMBF.  相似文献   
5.
6.
7.
The objective of this survey was to demonstrate whether a primary care track internal medicine residency program emphasizing community-based health care of the urban sick poor trains physicians who will continue to practice in general internal medicine or similar fields. Thirty-five primary care residents (100% of graduates) who trained from 1976 through 1993 in the Adult Primary Care Track of the Internal Medicine Residency Program at St. Vincent's Hospital, New York were used as participants.  相似文献   
8.
The present study establishes correlations of in vivo growth inhibition of a solid tumor, pancreatic ductal adenocarcinoma (Panc03), of mice with the steric and electrostatic fields and the hydrophobic parameter log P of a series (32) of 1-[[2-(dialkylamino)alkyl]amino]- 9H-thioxanthen-9-ones by the 3D-QSAR method comparative molecular field analysis (CoMFA). The template molecular model was hycanthone methanesulfonate (19), the structure of which had been established previously by X-ray crystallography. The hycanthone base is protonated at the terminal nitrogen N(2), and an intramolecular hydrogen bond is present between the proximal nitrogen N(1) and carbonyl oxygen O(1) atoms. Crystallographic data also indicate a planar arrangement of bonds around N(1). However, the molecular geometry of 19, optimized by semiempirical molecular orbital methods (PM3, MNDO, AM1), showed the expected trigonal-pyramidal configuration for N(1). A comparison of MO and ab initio methods applied to a model compound, 1-amino-9H-thioxanthen-9-one, led to the selection of PM3 as the method for full geometry optimization of first the cationic and then the neutral forms of 1-32, whereas AM1 provided atomic charges for these same structures save those incorporating a sulfonamide moiety (5, 7, 20, 25, 26, 29, 31, and 32). Acceptable values for the latter were obtained from ab initio calculations. Structures were aligned by minimizing root-mean-square (rms) differences in the fitting of structures to 19 using the FIT option of SYBYL. An alternative strategy of alignment, steric and electrostatic alignment (SEAL), was invoked to provide a comparison of statistical data generated with the rms alignment. The rms-fit alignment of structures produced slightly better cross-validated and conventional r2 values than those generated with the SEAL method. In addition, the rms-fit data indicate that a shift in the lattice of one-half of its spacing has a much smaller effect on the CoMFA data for a lattice of 1 A than one of 2 A. Inclusion of log P in a CoMFA of the neutral structures effected a small (ca. 8-10%) but significant improvement in cross-validated r2 values. The relative contributions of the hydrophobic effects and the steric and electrostatic fields to the conventional r2 values were 16%, 42%, and 42%, respectively. By contrast, incorporation of frontier molecular orbital (HOMO and LUMO) energies or their gaps in the PLS analyses failed to enhance correlation coefficients derived for either the charged or uncharged compounds.(ABSTRACT TRUNCATED AT 400 WORDS)  相似文献   
9.
10.
Five overlapping type 1 Epstein-Barr virus (EBV) DNA fragments constituting a complete replication- and transformation-competent genome were cloned into cosmids and transfected together into P3HR-1 cells, along with a plasmid encoding the Z immediate-early activator of EBV replication. P3HR-1 cells harbor a type 2 EBV which is unable to transform primary B lymphocytes because of a deletion of DNA encoding EBNA LP and EBNA 2, but the P3HR-1 EBV can provide replication functions in trans and can recombine with the transfected cosmids. EBV recombinants which have the type 1 EBNA LP and 2 genes from the transfected EcoRI-A cosmid DNA were selectively and clonally recovered by exploiting the unique ability of the recombinants to transform primary B lymphocytes into lymphoblastoid cell lines. PCR and immunoblot analyses for seven distinguishing markers of the type 1 transfected DNAs identified cell lines infected with EBV recombinants which had incorporated EBV DNA fragments beyond the transformation marker-rescuing EcoRI-A fragment. Approximately 10% of the transforming virus recombinants had markers mapping at 7, 46 to 52, 93 to 100, 108 to 110, 122, and 152 kbp from the 172-kbp transfected genome. These recombinants probably result from recombination among the transfected cosmid-cloned EBV DNA fragments. The one recombinant virus examined in detail by Southern blot analysis has all the polymorphisms characteristic of the transfected type 1 cosmid DNA and none characteristic of the type 2 P3HR-1 EBV DNA. This recombinant was wild type in primary B-lymphocyte infection, growth transformation, and lytic replication. Overall, the type 1 EBNA 3A gene was incorporated into 26% of the transformation marker-rescued recombinants, a frequency which was considerably higher than that observed in previous experiments with two-cosmid EBV DNA cotransfections into P3HR-1 cells (B. Tomkinson and E. Kieff, J. Virol. 66:780-789, 1992). Of the recombinants which had incorporated the marker-rescuing cosmid DNA fragment and the fragment encoding the type 1 EBNA 3A gene, most had incorporated markers from at least two other transfected cosmid DNA fragments, indicating a propensity for multiple homologous recombinations. The frequency of incorporation of the nonselected transfected type 1 EBNA 3C gene, which is near the end of two of the transfected cosmids, was 26% overall, versus 3% in previous experiments using transfections with two EBV DNA cosmids. In contrast, the frequency of incorporation of a 12-kb EBV DNA deletion which was near the end of two of the transfected cosmids was only 13%.(ABSTRACT TRUNCATED AT 400 WORDS)  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