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   1416篇
  免费   2篇
  国内免费   3篇
电工技术   10篇
综合类   1篇
化学工业   38篇
金属工艺   5篇
机械仪表   3篇
建筑科学   2篇
能源动力   3篇
轻工业   11篇
水利工程   2篇
石油天然气   9篇
无线电   8篇
一般工业技术   14篇
冶金工业   1310篇
原子能技术   4篇
自动化技术   1篇
  2023年   4篇
  2022年   9篇
  2021年   4篇
  2020年   2篇
  2018年   5篇
  2015年   2篇
  2014年   4篇
  2013年   9篇
  2012年   12篇
  2011年   6篇
  2010年   2篇
  2009年   5篇
  2008年   7篇
  2007年   3篇
  2006年   4篇
  2005年   1篇
  2004年   3篇
  2003年   3篇
  2002年   3篇
  2001年   3篇
  2000年   5篇
  1999年   38篇
  1998年   436篇
  1997年   216篇
  1996年   156篇
  1995年   70篇
  1994年   59篇
  1993年   97篇
  1992年   9篇
  1991年   14篇
  1990年   9篇
  1989年   12篇
  1988年   13篇
  1987年   15篇
  1986年   20篇
  1985年   18篇
  1984年   2篇
  1983年   2篇
  1982年   7篇
  1981年   4篇
  1980年   8篇
  1978年   4篇
  1977年   27篇
  1976年   77篇
  1975年   4篇
  1974年   2篇
  1973年   1篇
  1966年   1篇
  1964年   1篇
  1958年   1篇
排序方式: 共有1421条查询结果,搜索用时 15 毫秒
91.
Catalysis Letters - To avoid the aggregation problem and activity loss of nickel oxide (NiO) nanoparticles (NPs) in organic reactions, NiO NPs were incorporated into TUD-1 mesoporous material....  相似文献   
92.
Tobacco mosaic virus (TMV) derivatives that encode movement protein (MP) as a fusion to the green fluorescent protein (MP:GFP) were used in combination with antibody staining to identify host cell components to which MP and replicase accumulate in cells of infected Nicotiana benthamiana leaves and in infected BY-2 protoplasts. MP:GFP and replicase colocalized to the endoplasmic reticulum (ER; especially the cortical ER) and were present in large, irregularly shaped, ER-derived structures that may represent "viral factories." The ER-derived structures required an intact cytoskeleton, and microtubules appeared to redistribute MP:GFP from these sites during late stages of infection. In leaves, MP:GFP accumulated in plasmodesmata, whereas in protoplasts, the MP:GFP was targeted to distinct, punctate sites near the plasma membrane. Treating protoplasts with cytochalasin D and brefeldin A at the time of inoculation prevented the accumulation of MP:GFP at these sites. It is proposed that the punctate sites anchor the cortical ER to plasma membrane and are related to sites at which plasmodesmata form in walled cells. Hairlike structures containing MP:GFP appeared on the surface of some of the infected protoplasts and are reminiscent of similar structures induced by other plant viruses. We present a model that postulates the role of the ER and cytoskeleton in targeting the MP and viral ribonucleoprotein from sites of virus synthesis to the plasmodesmata through which infection is spread.  相似文献   
93.
94.
Investigations were carried out in a long term field experiment from 1976 to 1982, on a loamy sand soil to find out the fertilizer requirements of groundnut and wheat grown in fixed rotation. Application of 26 kgP/ha to wheat alone was found to be sufficient for both wheat and succeeding groundnut. Application of phosphorus to both wheat and groundnut did not result in extra beneficial effect over P application to wheat alone. However, application of 26 kg P/ha to groundnut alone was not sufficient for succeeding wheat. There was no response from K application (25 kg K/ha) in either of these two crops. Increasing the dose of N from 50–150 kg/ha to wheat significantly increased the grain yield of wheat but the pod yield of succeeding groundnut were markedly lowered. Response of wheat to 150 kg N/ha was more marked when P was also applied to wheat and response was less when P was applied to preceding groundnut alone. Zinc application at 6.25 kg/ha to wheat alone resulted in significant increase in grain yield of wheat and pod yield of succeeding groundnut.  相似文献   
95.
96.
R1 and R2 retrotransposable elements are stable components of the 28S rRNA genes of arthropods. While each retrotransposition event leads to incremental losses of rDNA unit expression, little is known about the selective consequences of these elements on the host genome. Previous reports suggested that in the abnormal abdomen (aa) phenotype of Drosophila mercatorum, high levels of rDNA insertions (R1) in conjunction with the under-replication locus (ur), enable the utilization of different ecological conditions via a population level shift to younger age. We have sequenced the R1 and R2 elements of D. mercatorum and show that the levels of R1- and R2-inserted rDNA units were inaccurately scored in the original studies of aa, leading to several misinterpretations. In particular, contrary to earlier reports, aa flies differentially underreplicate R1- and R2-inserted rDNA units, like other species of Drosophila. However, aa flies do not undergo the lower level of underreplication of their functional rDNA units (general underreplication) that is seen in wild-type strains. The lack of general underreplication is expected to confer a selective advantage and, thus, can be interpreted as an adaptation to overcome high levels of R1 and R2 insertions. These results allow us to reconcile some of the apparently contradictory effects of aa and the bobbed phenotype found in other species of Drosophila.  相似文献   
97.
X-ray diffraction analysis of poly d(AI).poly d(CT) in oriented and polycrystalline fibers has revealed the DNA structure to be a 10-fold, right-handed, antiparallel, Watson-Crick base paired double helix in two distinct packing arrangements corresponding to one and two helices, respectively, in the unit cell. The helix pitch is 32.1 A and 32.4 A in the two cases, almost 1.5 A shorter than in classical B-DNA. The resulting B'-DNA geometry, described in terms of a tetranucleotide repeat which is conformationally similar to B-DNA, has its minor groove closely shut and major groove correspondingly widened, thus striking a sharp morphological contrast to B-DNA. According to difference electron density maps, a spine of hydration along the minor groove connects both strands and provides structural stability; ordered sodium ions and water molecules are actively involved in bridging the phosphate groups of neighboring helices. The crystallographic R-values for these two allomorphs are 0.26 and 0.20, respectively, for data up to 3.0 A resolution.  相似文献   
98.
This article reviews the scientific literature in several areas important to the delivery of palliative care: multicultural issues, education, comprehensive outcome measures and ethics. Most of the research can be classified as fundamental rather than intervention research according to the Cancer Control Framework of the National Cancer Institute of Canada. Desired outcomes of interventions are most often defined from the health care professional's perspective but need to be defined from the patient's perspective. In areas such as multicultural issues and the effect of the volunteer on the patient, there is almost no research. The complexity of studying the best way to deliver palliative care would benefit from the input of colleagues who have experience addressing these issues in other patient populations.  相似文献   
99.
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