全文获取类型
收费全文 | 3372篇 |
免费 | 288篇 |
国内免费 | 339篇 |
专业分类
化学 | 571篇 |
晶体学 | 19篇 |
力学 | 78篇 |
综合类 | 121篇 |
数学 | 2277篇 |
物理学 | 933篇 |
出版年
2024年 | 4篇 |
2023年 | 21篇 |
2022年 | 40篇 |
2021年 | 68篇 |
2020年 | 69篇 |
2019年 | 66篇 |
2018年 | 68篇 |
2017年 | 73篇 |
2016年 | 77篇 |
2015年 | 54篇 |
2014年 | 127篇 |
2013年 | 258篇 |
2012年 | 126篇 |
2011年 | 184篇 |
2010年 | 162篇 |
2009年 | 330篇 |
2008年 | 314篇 |
2007年 | 287篇 |
2006年 | 233篇 |
2005年 | 163篇 |
2004年 | 171篇 |
2003年 | 179篇 |
2002年 | 175篇 |
2001年 | 110篇 |
2000年 | 86篇 |
1999年 | 104篇 |
1998年 | 90篇 |
1997年 | 82篇 |
1996年 | 44篇 |
1995年 | 50篇 |
1994年 | 36篇 |
1993年 | 18篇 |
1992年 | 20篇 |
1991年 | 13篇 |
1990年 | 17篇 |
1989年 | 13篇 |
1988年 | 14篇 |
1987年 | 5篇 |
1986年 | 7篇 |
1985年 | 7篇 |
1984年 | 9篇 |
1983年 | 4篇 |
1982年 | 3篇 |
1981年 | 5篇 |
1979年 | 2篇 |
1977年 | 2篇 |
1974年 | 2篇 |
1970年 | 1篇 |
1959年 | 1篇 |
1936年 | 2篇 |
排序方式: 共有3999条查询结果,搜索用时 15 毫秒
81.
82.
83.
Two published procedures for glass capillary column production are applied to produce capillaries for chromatography of polar natural compounds. Soda lime glass capillaries, after leaching with aqueous HCL, are either treated with colloidal silicic acid or with barium carbonate and coated with either Silar 7CP or SE 52. A test mixture as well as polar carbohydrate and peptide mixtures are chromatographed on the different columns and their chromatographic properties are evaluated. Combined capillary gas chromatography-electron impact and chemical ionization mass spectrometry are used for identification of the peptide sequence. 相似文献
84.
Yong Deng Da Cheng Yang Yi Shen Yu Guo Zhong 《中国化学快报》2007,18(1):7-9
Based on the structure-activity relationships and antiangiogenic mechanism of RGD-containing peptides,a series of 5-amino- 1,3-dihydro-1,3-dioxo-2H-isoindole derivatives were synthesized.The structures were characterized by ~1H NMR,MS and elementary analysis.There ability to inhibit angiogenesis were evaluated by chick embryo chorioallantoic membrane assay at 10~(-5) mol/L.Compounds 7a and 7b displayed obvious antiangiogenic activity. 相似文献
85.
Hans-Joachim Böhm 《Journal of computer-aided molecular design》1992,6(1):61-78
Summary A new computer program is described, which positions small molecules into clefts of protein structures (e.g. an active site of an enzyme) in such a way that hydrogen bonds can be formed with the enzyme and hydrophobic pockets are filled with hydrophobic groups. The program works in three steps. First it calculates interaction sites, which are discrete positions in space suitable to form hydrogen bonds or to fill a hydrophobic pocket. The interaction sites are derived from distributions of nonbonded contacts generated by a search through the Cambridge Structural Database. An alternative route to generate the interaction sites is the use of rules. The second step is the fit of molecular fragments onto the interaction sites. Currently we use a library of 600 fragments for the fitting. The final step in the present program is the connection of some or all of the fitted fragments to a single molecule. This is done by bridge fragments. Applications are presented for the crystal packing of benzoic acid and the enzymes dihydrofolate reductase and trypsin. 相似文献
86.
87.
投料顺序对动态硫化PP/EPDM性能影响及其机理的研究 总被引:12,自引:0,他引:12
针对PP降解在PP/EPDM动态硫化中对体系产生的不利影响。考察了四种不同投料顺序对PP/EPDM动态硫化物的冲击韧性,加工流动性,交联程度和断面形貌等宏观和微观性能,并进行了不同EPDM含量的动态硫化和非硫化PP/EPDM的性能比较。结果表明,优化投料顺序能实现对动态硫化体系中化学反应对象和化学反应程度的有效干预。 相似文献
88.
G. Wu R. M. Izatt M. L. Bruening W. Jiang H. Azab K. E. Krakowiak J. S. Bradshaw 《Journal of inclusion phenomena and macrocyclic chemistry》1992,13(2):121-127
The aqueous protonation and anion-binding SeO
2
–/4
SO
2–
4
, and NO
–
3
) constants of the macrocyclic polyamine ligand, dipyridino-hexaaza-28-crown-8(L), were measured in 0.1M KCl using a potentiometric titration technique. The protonation sequence of the aza groups of L was studied in D2O from the chemical shifts of the nonlabile protons so as to find the charge distribution geometry as a function of pD. The study indicates that in 0.1M KC1 fully protonated L forms stable l: 1 complexes with SeO
2–
4
(logK=3.68) and SO
2–
4
(logK=3.55), but not with NO
–
3
(logK < l.5). All of the amine pK values were above 6.3, thus allowing the use of the protonated form of this ligand over a wide pH range. 相似文献
89.
Summary A genetic algorithm has been designed which generates molecular structures within constraints. The constraints may be any useful function, for example an enzyme active site, a pharmacophore or molecular properties from pattern recognition or rule-induction analyses. The starting point may be random or may utilise known molecules. These are modified to grow into families of structures which, using the evolutionary operators of selection, crossover and mutation evolve to better fit the constraints. The basis of the algorithm is described together with some applications in lead generation, 3D database construction and drug design. Genetic algorithms of this type may have wider applications in chemistry, for example in the design and optimisation of new polymers, materials (e.g. superconducting materials) or synthetic enzymes. 相似文献
90.
Tamás F. Móri 《Journal of Theoretical Probability》1995,8(1):139-164
Considering an infinite string of i.i.d. random letters drawn from a finite alphabet we define the cover timeW
n
as the number of random letters needed until each pattern of lenghtn appears at least once as a substring. Sharp weak and a.s. limit results onW
n
are known in the symmetric case, i.e., when the random letters are uniformly distributed over the alphabet. In this paper we determine the limit distribution ofW
n
in the nonsymmetric case asn. Generalizations in terms of point processes are also proved.Dedicated to Endre Csáki on his 60th birthday. 相似文献