首页 | 官方网站   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   4092篇
  免费   33篇
  国内免费   3篇
工业技术   4128篇
  2021年   13篇
  2020年   10篇
  2019年   14篇
  2018年   16篇
  2017年   24篇
  2016年   16篇
  2015年   17篇
  2014年   28篇
  2013年   99篇
  2012年   57篇
  2011年   63篇
  2010年   50篇
  2009年   49篇
  2008年   63篇
  2007年   61篇
  2006年   54篇
  2005年   56篇
  2004年   51篇
  2003年   36篇
  2002年   57篇
  2001年   49篇
  2000年   48篇
  1999年   118篇
  1998年   783篇
  1997年   458篇
  1996年   292篇
  1995年   183篇
  1994年   139篇
  1993年   170篇
  1992年   39篇
  1991年   54篇
  1990年   49篇
  1989年   45篇
  1988年   53篇
  1987年   38篇
  1986年   47篇
  1985年   43篇
  1984年   36篇
  1983年   34篇
  1982年   25篇
  1981年   53篇
  1980年   41篇
  1979年   22篇
  1978年   30篇
  1977年   95篇
  1976年   208篇
  1975年   22篇
  1974年   21篇
  1973年   18篇
  1967年   8篇
排序方式: 共有4128条查询结果,搜索用时 93 毫秒
31.
Abstract

Strategic management was introduced as a critical component of Australian local government reform during the 1990s. In addition to encouraging efficiency and effectiveness of operation, it was also intended to promote participatory democracy within local authorities. The paper explores the extent to which this objective has been achieved through an analysis of twenty‐five New South Wales municipalities. Discussion concludes that while strategic management has enhanced community involvement in local governance, it cannot be a substitute for traditional democratic processes.  相似文献   
32.
PET短纤维和长丝:生产工艺的发展趋势   总被引:2,自引:0,他引:2  
聚酯短纤维和长丝的消费不断增长,这给商业增长提供了巨大的机会,但同时,世界范围的竞争日趋激烈。今天为了保持市场竞争力,作出正确决定变得越来越重要。本文的目的是从技术角度剖析赢得经济挑战的一些基本因素。  相似文献   
33.
In several organisms, the success of a male's sperm in multiply inseminated females depends on the male's genotype. In Drosophila, the female also plays a role in determining which sperm are successful. Pairwise tests among six isogenic lines of Drosophila melanogaster were performed to determine whether there is a genotype-specific interaction in the success of sperm. The success of a particular male's sperm was found to depend on the genotype of the female with which he mates, providing evidence for an interaction with profound evolutionary consequences.  相似文献   
34.

Abstract  

Catalytic performance of solid supported monovanadate catalysts toward oxidation of propane is significantly affected by the templating effect of: (1) pretreatment of the solid support with calixarene derivatives before deposition of ammonium vanadate, (2) direct deposition of vanadyl phthalocyanine as the vanadate precursor. This effect is believed to be linked to the accessibility of the active sites, and was studied in comparison with a reference mesoporous support.  相似文献   
35.
36.
Complexes composed of peptide ligand for the serpin enzyme complex receptor covalently coupled to poly-L-lysine condensed by charge interaction with plasmid DNA direct gene transfer into receptor bearing cells. We compared intensity and duration of reporter gene expression in vitro and in vivo from serpin-enzyme receptor-directed gene transfer complexes prepared with poly-L-lysine of different chain lengths. When substituted with linker and ligand to comparable extents, DNA complexes containing short chain poly-L-lysine were larger and gave higher peak expression but significantly shorter duration of expression than those containing long chain poly-L-lysine. Both peak expression and duration of expression exceeded that observed with Lipofectin. Neither naked DNA nor DNA complexed with unsubstituted polylysine was effective in gene transfer. For in vivo experiments, complexes containing optimal ligand and degree of substitution (based on in vitro data, peptide C105Y, 11 ligands/plasmid DNA molecule) were prepared with either short chain or long chain polylysine and a beta-galactosidase expression plasmid. Following injection into the tail veins of mice, longer chain complexes gave significantly higher expression of reporter gene in lung and spleen that lasted for a significantly longer period of time than the shorter chain complexes. The short chain poly-L-lysine-DNA complexes were larger in diameter, as assessed by electron microscopy or atomic force microscopy, and gave less protection against DNase digestion in vitro than longer chain complexes. Thus, for gene transfer complexes directed at the serpin enzyme complex receptor, longer chain poly-L-lysine gave a much longer duration of expression both in vitro and in vivo. We speculate that this may be due to protection against degradation afforded the plasmid DNA by the tighter compaction produced by long chain poly-L-lysine.  相似文献   
37.
38.
This study evaluated the use of lactic acid to decontaminate Listeria monocytogenes andEdwardsiella tarda attached to catfish skin with or without mucus. At the highest inoculum levels (104–105cfu skin−1), lactic acid (0·5–2·0%) exposure for 10 min reduced counts of L. monocytogenes firmly attached to catfish skin by 0·9–>1·9 log10cfu skin−1and cells loosely attached by 2·7–>3·7 logs. Counts of E. tarda firmly attached to catfish skin were reduced by 0·9–>3·0 logs and cells loosely attached by 1·5–>3·5 logs. Overall bacterial numbers of lactic acid-treated cells that were firmly attached to skin with mucus were higher than on skin without mucus. Firmly attached L. monocytogenes was more resistant to lactic acid than was firmly attached E. tarda. Catfish skin mucus decreased the antimicrobial effect of lactic acid against attached L. monocytogenes and E. tarda.  相似文献   
39.
On a Windows platform it is possible to inject a DLL into a running process creating a new thread of execution within an authorized process. Security tools monitoring or examining DLLs loaded into the memory space of a given process rely on policies to determine the validity of the library. Two approaches to the policy specification include “all or nothing” and “per executable” rules also referred to as a run-time security policy. Developing the run-time policy requires the running of every executable for a period of time to train the system. An alternative to the training method of the run-time approach is to determine ahead of time which DLL should be loaded before execution. A tool called LibMon was developed to monitor loading of libraries by running applications. A heuristic search algorithm was created based on the analysis of the data collected with LibMon.  相似文献   
40.
This paper assesses the diagenetic history of potential fluvial hydrocarbon reservoir rocks deposited within incised valley systems of the Lower Carboniferous Marar Formation in western Libya. Outcrop data were collected in the Tinedhan Anticline, located at the southern margin of the Ghadames Basin. Four discrete intervals with channelized sandstones were identified in a section dominated by alternating offshore mudstones and shallow-marine clastics. The incised channels were cut during major sea-level lowstands, and filled by fluvial sandstone packages up to 50 m thick. Fifty-eight samples from four different localities, representing three lowstand systems tracts, were analysed to obtain a statistically meaningful mineralogical and compositional dataset. In addition to burial compaction, three main diagenetic events influenced the reservoir quality of the sandstones. Firstly, early eodiagenesis involved kaolinitization of plagioclase grains. This began before subsequent calcite cementation, probably as a result of flushing by meteoric pore-waters. The deformation of kaolinite during later compaction resulted in the formation of pseudomatrix which further reduced porosity and permeability. Kaolinite is commonly transformed to illite at temperatures above 140°C in the presence of K-feldspar. Although K-feldspar was recorded in the samples, no illite was observed, suggesting that the Lower Carboniferous strata in the study area were not buried in excess of approximately 3.5 km. The second diagenetic phase was the precipitation of calcite cement, present either dispersed throughout the sandbodies or as concretions up to 2 m across, in both cases reducing reservoir quality. The high intergranular volumes (IGV) of calcite-cemented sandstones (ranging between 35% and 40%) suggest that cementation occurred at burial depths of <500 m. Sandstones without calcite cement have lower IGV of between 17% and 25% as a result of mechanical and chemical compaction. Stable C and O isotope analysis of the calcite cement also supports precipitation at shallow burial depths, indicating a meteoric pore-water source for the calcite. The third and final diagenetic stage was partial chloritisation of kaolinite during meso-diagenesis. The elevated temperatures required for this transformation indicate burial to a minimum depth of approximately 2.5 km, which is consistent with the compaction data. Despite these diagenetic effects, the fluvial sandstones have an average porosity of 12%, with a range from 0.5% up to 25%. Permeability measurements on four sandstone samples indicate that the development of pseudomatrix did not reduce permeability significantly.  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-23

京公网安备 11010802026262号