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   30018篇
  免费   1160篇
  国内免费   437篇
化学   20316篇
晶体学   305篇
力学   1059篇
综合类   16篇
数学   2635篇
物理学   7284篇
  2023年   183篇
  2022年   462篇
  2021年   583篇
  2020年   522篇
  2019年   554篇
  2018年   418篇
  2017年   382篇
  2016年   849篇
  2015年   777篇
  2014年   953篇
  2013年   1693篇
  2012年   2188篇
  2011年   2356篇
  2010年   1447篇
  2009年   1303篇
  2008年   1924篇
  2007年   1782篇
  2006年   1666篇
  2005年   1560篇
  2004年   1363篇
  2003年   1078篇
  2002年   1054篇
  2001年   735篇
  2000年   618篇
  1999年   383篇
  1998年   290篇
  1997年   314篇
  1996年   359篇
  1995年   282篇
  1994年   301篇
  1993年   291篇
  1992年   283篇
  1991年   222篇
  1990年   169篇
  1989年   150篇
  1988年   145篇
  1987年   129篇
  1986年   102篇
  1985年   179篇
  1984年   120篇
  1983年   102篇
  1982年   127篇
  1981年   91篇
  1980年   104篇
  1978年   103篇
  1977年   133篇
  1976年   112篇
  1975年   119篇
  1974年   90篇
  1973年   108篇
排序方式: 共有10000条查询结果,搜索用时 9 毫秒
41.
42.
The neutron irradiated potassium hexacyanoferrate(III) solutions were analyzed for Fe(CN)64?, Fe(CN)63?, and Prussian blue. The retention values (1.1%) were constant throughout the pH and concentration ranges studied, and did not change with the length of irradiation. The complex behavior of the radiochemical yield of the Fe(CN)64? and Prussian blue was attributed to the competition of the various reactions involved in the irradiation.  相似文献   
43.
44.
It is conceivable that the high-T c superconducting perovskites are conventional electronphonon superconductors. In this case one expects significant strong-coupling effects because of the unusually high ratiok B T c / of the order 0.1 and greater. We use a set of reasonable models for the Eliashberg function 2 F() (which takes into account available information on the phonon spectra and which fit the measuredT c 's) and calculate strong-coupling effects in the specific heatc s (T)/T c , the ratio 0/k B T c , the critical fieldsH c (T) andH c2 (T) including Pauli limiting, and other measurable quantities. Strongcoupling corrections turn out to be in the range of 0 to about 100%, depending on the quantity of interest. We discuss the perspectives of using strong-coupling effects as indicators for conventional electron-phonon superconductivity in the new materials.  相似文献   
45.
46.
A rapid flow-injection sandwich enzyme immunoassay suitable for the direct determination of proteins in biological samples is described. The proposed system utilizes highly active adenosine deaminase—antibody conjugates in conjunction with a flow-through immunoreactor and an ammonium ion-selective potentiometric detector. After appropriate sample/reagent injection steps, the enzyme activity bound to the reactor is measured by diverting a coninuously flowing stream of substrate (adenosine) through the packed immunocolumn and detecting liberated ammonium ions downstream with a tubular ammonium ion-selective electrode. The bound enzyme activity is directly proportional to the concentration of analyte in the original sample. By using non-equilibrium flow-rates of sample and reagent slugs, a single protein assay takes less than 12 min, including regeneration of the reactor. The proposed method is shown to be selective, reproducible and capable of determining accurately the model protein (human IgC) at sub-μg ml?1 concentrations.  相似文献   
47.
K K Lee  A E Ellis 《Electrophoresis》1989,10(10):729-731
A rapid and sensitive silver-lipopolysaccharide staining method has been developed by using PhastSystem. The total time of the procedure (including time of Phastgel electrophoresis) is within 2 h. It is at least 10 times faster than the previous reported methods and the sensitivity is also increased.  相似文献   
48.
Applied Biochemistry and Biotechnology - By inserting metallocatalysts (such as platinum, osmium, or ruthenium) at the reducing site of photosystem I (PSI), electrons that emerge from PSI can be...  相似文献   
49.
Expense and inconvenience have restricted the use of the filtered xenon are lamp (solar simulator) as a UV source for conducting large-scale animal studies. Because sunscreen immunoprotective levels are significantly affected by the UV power spectrum of the source it is imperative that a solar simulating source be used for accurate measurements of sunscreen protection levels that are relevant to human UV exposures from sunlight. However, relatively inexpensive sunlamps, e. g. the UVA-340, that emit a UV power spectrum similar to that of a solar simulator are available. Unlike FS-type UVB sunlamps, which have a significant amount of effective immunosuppressive nonsolar UV energy at wavelengths below 295 nm, the immunosuppression effectiveness spectrum of UVA-340 sunlamps was nearly identical to that of a solar simulator. The purpose of this study was to evaluate this sunlamp for conducting photoimmunological and sunscreen immune protection studies. Groups of C3H mice were exposed to a range of UVA-340 sunlamp doses (0.25 KJ/m2 to 20.0 KJ/m2) to establish a dose-response curve and determine the minimum immune suppression dose (MISD) for induction of local-type suppression of contact hypersensitivity (CH). The MISD, defined as the lowest UV dose given to produce ~50% suppression of the CH response in mice, was determined to be 1.0 kJ/m2 for UVA-340 sunlamps. Immune protection tests on four marketed sunscreen lotions (sun protection factors [SPF] 4, 8, 15 and 30) were then conducted with UVA-340 sunlamps using MISD as the endpoint. The immune protection factors for these sunscreens were equivalent to the level of protection predicated by their labeled SPF. These results are similar to those we have previously obtained using a solar simulator. We conclude from these data that the immunosuppressive effects of UVA-340 sunlamps are similar to those of a solar simulator; however, further studies are needed to determine if UVA-340, or similar, sunlamps are a viable alternative to the solar simulator for conducting large-scale animal experiments that require a relevant UV solar spectrum.  相似文献   
50.
Novel palladium hollow spheres were synthesized using silica spheres as a template, and they were successfully applied as recyclable heterogeneous catalysts for Suzuki cross coupling reactions.  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