全文获取类型
收费全文 | 58904篇 |
免费 | 775篇 |
国内免费 | 302篇 |
专业分类
化学 | 27349篇 |
晶体学 | 1026篇 |
力学 | 3203篇 |
综合类 | 8篇 |
数学 | 4656篇 |
物理学 | 23739篇 |
出版年
2022年 | 535篇 |
2021年 | 479篇 |
2020年 | 447篇 |
2019年 | 424篇 |
2018年 | 575篇 |
2017年 | 496篇 |
2016年 | 891篇 |
2015年 | 634篇 |
2014年 | 988篇 |
2013年 | 2498篇 |
2012年 | 2331篇 |
2011年 | 3009篇 |
2010年 | 2123篇 |
2009年 | 2172篇 |
2008年 | 2749篇 |
2007年 | 2588篇 |
2006年 | 2451篇 |
2005年 | 2175篇 |
2004年 | 1986篇 |
2003年 | 1756篇 |
2002年 | 1646篇 |
2001年 | 3005篇 |
2000年 | 2150篇 |
1999年 | 1555篇 |
1998年 | 1081篇 |
1997年 | 1059篇 |
1996年 | 884篇 |
1995年 | 783篇 |
1994年 | 704篇 |
1993年 | 623篇 |
1992年 | 951篇 |
1991年 | 946篇 |
1990年 | 849篇 |
1989年 | 747篇 |
1988年 | 731篇 |
1987年 | 795篇 |
1986年 | 654篇 |
1985年 | 882篇 |
1984年 | 828篇 |
1983年 | 568篇 |
1982年 | 562篇 |
1981年 | 533篇 |
1980年 | 496篇 |
1979年 | 620篇 |
1978年 | 650篇 |
1977年 | 660篇 |
1976年 | 575篇 |
1975年 | 481篇 |
1974年 | 521篇 |
1973年 | 450篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
Pandya SU Garçon C Chavant PY Py S Vallée Y 《Chemical communications (Cambridge, England)》2001,(18):1806-1807
The vinylzinc reagents derived from hydrozirconation of alkynes and transmetallation add readily to nitrones to yield pure (E)-N-allylhydroxylamines; some of these rearrange into O-allylhydroxylamines. 相似文献
992.
A new chromogenic reagent tribromocarboxyarsenazo has been synthesized and the chromogenic reaction of this reagent with zirconium studied. In the medium of 0.5 mol/1 HCl, a blue complex is formed by the reaction of zirconium with tribromocarboxyarsenazo. The maximum absorption of the complex is at 633 nm, and the apparent molar absorptivity is 4.8 x 10(4) 1/mol/cm. Beer's law is obeyed over the zirconium concentration range 0-18, mug/25 ml. The method has been applied to the determination of zirconium in aluminum, copper and magnesium alloys with satisfactory results. 相似文献
993.
994.
A rapid and sensitive high-performance liquid chromatographic method is described for simultaneous determination of isoniazid methanesulphonate (IHMS) and its metabolites, such as isoniazid (INH) and acetylisoniazid (AcINH) in rabbit blood. According to stability studies, IHMS was most stable at pH 3-5. After acidifying the blood to pH 5.0, a suitable amount of acetonitrile was added to the supernatant for extraction and niacinamide served as an internal standard. After evaporation, the residue was reconstituted with phosphate buffer and aliquots of this solution were separated on a reversed-phase phenyl column by a mobile phase consisting of 0.25 mM tetrabutylammonium phosphate as a paired-ion reagent. UV detection was performed at 280 nm. Under these conditions, the between-run coefficients of variation of IHMS, INH and AcINH from 1 to 25 microns/ml were 4.7 +/- 2.5, 5.4 +/- 1.0 and 5.1 +/- 3.1%, respectively. Hence this sensitive, reproducible and accurate method was suitable for pharmacokinetic studies of IHMS. 相似文献
995.
996.
Wesley Y. Yoshida Kit K. Lee Anthony R. Carroll Paul J. Scheuer 《Helvetica chimica acta》1992,75(5):1721-1725
Two cytotoxic triphenylpyrrolo-oxazinones were isolated from a tunicate and their structures elucidated by spectral methods. Lukianol A ( = 3,7,8-tris(4-hydroxyphenyl)pyrrolo[2,1-c][1,4]oxazin-1 (1H)-one; 1 ) had MIC of 1 μg/ml in KB cytotoxicity tests; MIC value for 2 was 100 μg/ml. 相似文献
997.
Nanofabrication: conventional and nonconventional methods 总被引:4,自引:0,他引:4
Nanofabrication is playing an ever increasing role in science and technology on the nanometer scale and will soon allow us to build systems of the same complexity as found in nature. Conventional methods that emerged from microelectronics are now used for the fabrication of structures for integrated circuits, microelectro-mechanical systems, microoptics and microanalytical devices. Nonconventional or alternative approaches have changed the way we pattern very fine structures and have brought about a new appreciation of simple and low-cost techniques. We present an overview of some of these methods, paying particular attention to those which enable large-scale production of lithographic patterns. We preface the review with a brief primer on lithography and pattern transfer concepts. After reviewing the various patterning techniques, we discuss some recent application issues in the fields of microelectronics, optoelectronics, magnetism as well as in biology and biochemistry. 相似文献
998.
Peyrin E Guillaume YC Grosset C Ravel A Villet A Garrel C Alary J Favier A 《Journal of chromatography. A》2000,886(1-2):1-7
Slalom chromatography (SC) is an alternative chromatographic procedure for the separation of relatively large double-stranded DNA molecules and is based on a new principle. The retardation of the DNA fragments from the cleavage of the Lambda DNA by the KpnI restriction enzyme was studied using an acetonitrile-phosphate buffer as a mobile phase with various concentrations of viscosity modifier (i.e. glycerol) and a C1 column as a stationary phase. The DNA molecule retention was accurately described over the glycerol concentration range using a model previously established. It was shown that the eluent viscosity increase enhanced the slalom chromatographic capacity to separate the DNA fragments. A connection between SC and 'hydrodynamic chromatography' processes was predicted to link the two processes in a global separation mechanism based on a non-equilibrium principle. 相似文献
999.
Stress fields between interacting small particles ( approximately 100 nm) have been investigated by transmission electron microscopy. The background for these TEM observations is discussed in terms of adhesion stress fields (due to surface forces), the action of an applied point force, possibly magnetic, and dislocations or misfit strains due to an unfavorable matching of crystal lattices at the grain boundary. A further explanation might be sought along the line "squeezed-in oxide" which can be visualized as a coherent particle or a dislocation loop. Accompanying theoretical calculations have been performed and compared with the experimental results. 相似文献
1000.
Lesaicherre ML Lue RY Chen GY Zhu Q Yao SQ 《Journal of the American Chemical Society》2002,124(30):8768-8769
We report here the first example using an intein-mediated expression system to generate biotinylated proteins suitable for immobilization onto avidin-functionalized glass slides. With this novel array, proteins are site-specifically immobilized on the glass surface and are able to retain their native activity. The advantage of the avidin/biotin linkage over his-tag/Ni-NTA strategies for protein immobilization is highlighted by its ability to withstand a variety of chemical conditions, which makes this new protein array compatible with most biological assays. 相似文献