全文获取类型
收费全文 | 29061篇 |
免费 | 698篇 |
国内免费 | 230篇 |
专业分类
化学 | 19742篇 |
晶体学 | 130篇 |
力学 | 649篇 |
综合类 | 1篇 |
数学 | 5479篇 |
物理学 | 3988篇 |
出版年
2022年 | 185篇 |
2021年 | 276篇 |
2020年 | 347篇 |
2019年 | 314篇 |
2018年 | 278篇 |
2017年 | 294篇 |
2016年 | 601篇 |
2015年 | 622篇 |
2014年 | 659篇 |
2013年 | 1419篇 |
2012年 | 1412篇 |
2011年 | 1712篇 |
2010年 | 960篇 |
2009年 | 819篇 |
2008年 | 1470篇 |
2007年 | 1475篇 |
2006年 | 1563篇 |
2005年 | 1408篇 |
2004年 | 1335篇 |
2003年 | 1104篇 |
2002年 | 1053篇 |
2001年 | 456篇 |
2000年 | 410篇 |
1999年 | 398篇 |
1998年 | 387篇 |
1997年 | 433篇 |
1996年 | 402篇 |
1995年 | 363篇 |
1994年 | 392篇 |
1993年 | 347篇 |
1992年 | 324篇 |
1991年 | 323篇 |
1990年 | 284篇 |
1989年 | 285篇 |
1988年 | 271篇 |
1987年 | 228篇 |
1986年 | 250篇 |
1985年 | 367篇 |
1984年 | 380篇 |
1983年 | 324篇 |
1982年 | 356篇 |
1981年 | 330篇 |
1980年 | 349篇 |
1979年 | 279篇 |
1978年 | 309篇 |
1977年 | 288篇 |
1976年 | 233篇 |
1975年 | 198篇 |
1974年 | 203篇 |
1973年 | 167篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
Guido Momerency Karel Van Cauwenberghe Ernst A. De Bruijn Allan T. Van Oosterom Martin S. Highley Peter G. Harper 《Journal of separation science》1994,17(9):655-661
A method is described for the determination of the antitumor agent iphosphamide and seven of its metabolites in the plasma of cancer patients by multiple ion monitoring (MIM) GC-MS, mainly using the electron capture chemical ionization mode, of stable methyl and/or trifluoroacetyl derivatives. The metabolites determined were 2- and 3-dechloroethyliphosphamide, 4-ketoiphosphamide, carboxyiphosphamide, iphosphamide mustard, and two previously undetected metabolites, chloroethylamine and 1,3-oxazolidine-2-one. The isolation of the acidic and neutral metabolites was performed by solid phase extraction on to C18 adsorbent at pH 4. The weakly acidic iphosphamide mustard, isolated under these conditions with a yield of ca 50%, was measured as a stable methyltrifluoroacetyl derivative, in contrast to the corresponding phosphoramide mustard of the isomer cyclophosphamide which decomposes during derivatization. Chloroethylamine and 1,3-oxazolidine-2-one were isolated with high yield by liquid extraction with ethyl acetate at pH 10. Selective measurement of several metabolite derivatives with similar retention times was performed by multiple ion monitoring MS of specific ion masses, using a methyl phenyl siloxane capillary column previously employed in the study of cyclophosphamide metabolites. Quantitation of metabolites in patient plasma samples could be performed in the concentration range 3 ng to 20 μg per ml of original plasma. 相似文献
92.
93.
94.
The melting behaviour, some phase boundaries and the lattice parameters in the region of the NiAs-type phase in the ternary system cobalt-antimony-tellurium have been determined by differential thermal analysis and X-ray diffraction. A projection of the liquidus surface and the phase relationships in different sections with constant antimony/tellurium ratios are presented. The peculiar variation of the lattice parameters with the composition of the nonstoichiometric NiAs-type phase is discussed in terms of the defect structure.Dedicated to Prof. K. L. Komarek on the occasion of his 65th birthday 相似文献
95.
What is the maximum number of unit distances between the vertices of a convex n-gon in the plane? We review known partial results for this and other open questions on multiple occurrences of the same interpoint distance in finite planar subsets. Some new results are proved for small n. Challenging conjectures, both old and new, are highlighted. 相似文献
96.
Katalytische Epoxidierung und 1,2‐Dihydroxylierung von Olefinen mit Bispidin‐Eisen(II)/H2O2‐Systemen
97.
Marko D. Mihovilovic Bernhard Müller Markus Spina Arjumand I. Durrani Peter Stanetty Georg Dazinger Karl Kirchner 《Monatshefte für Chemie / Chemical Monthly》2006,137(6):785-794
Summary. Recombinant Escherichia coli overexpressing Pseudomonas sp. NCIMB 9872 cyclopentanone monooxygenase (CPMO, EC 1.14.13.16) and Acinetobacter sp. NCIMB 9871 cyclohexanone monooxygenase (CHMO, EC 1.14.13.22) have been utilized in whole-cell Baeyer-Villiger biotransformations of prochiral bicycloketones. A significant difference in substrate acceptance and stereoselectivity was
observed for bicyclo[3.3.0] and bicyclo[4.3.0] substrates. A plausible mechanism of these transformations was established
by means of high level DFT/B3LYP calculations suggesting an essential difference in electronic requirements for a successful
enzymatic conversion, which was similarly encountered in recombinant whole-cell mediated biooxidations. Some of the lactones
produced in the biocatalytic Baeyer-Villiger oxidation represent key intermediates for the synthesis of indole alkaloids. 相似文献
98.
99.
The reduction of chromate by glutathione, its mono- and diethyl esters,
-cysteine, 2-mercapto-propionic acid and mercapto-succinic acid has been studied. The empirical rate law kobs = ab[Thiol]2/(1 + b[Thiol]) is obeyed by all of these thiols, at neutral pH. No evidence could be obtained for a first-order pathway in glutathione under these conditions. These observations are used to comment on the stability of intermediates potentially important in explaining chromate toxicity. 相似文献
100.