全文获取类型
收费全文 | 20219篇 |
免费 | 771篇 |
国内免费 | 2352篇 |
专业分类
化学 | 11378篇 |
晶体学 | 154篇 |
力学 | 164篇 |
综合类 | 204篇 |
数学 | 882篇 |
物理学 | 3195篇 |
综合类 | 7365篇 |
出版年
2023年 | 143篇 |
2022年 | 263篇 |
2021年 | 202篇 |
2020年 | 265篇 |
2019年 | 276篇 |
2018年 | 215篇 |
2017年 | 305篇 |
2016年 | 358篇 |
2015年 | 365篇 |
2014年 | 877篇 |
2013年 | 1371篇 |
2012年 | 1192篇 |
2011年 | 884篇 |
2010年 | 767篇 |
2009年 | 1084篇 |
2008年 | 1192篇 |
2007年 | 1440篇 |
2006年 | 1366篇 |
2005年 | 1352篇 |
2004年 | 982篇 |
2003年 | 906篇 |
2002年 | 615篇 |
2001年 | 509篇 |
2000年 | 1488篇 |
1999年 | 1140篇 |
1998年 | 979篇 |
1997年 | 393篇 |
1996年 | 363篇 |
1995年 | 366篇 |
1994年 | 328篇 |
1993年 | 268篇 |
1992年 | 219篇 |
1991年 | 176篇 |
1990年 | 158篇 |
1989年 | 107篇 |
1988年 | 73篇 |
1987年 | 55篇 |
1986年 | 37篇 |
1985年 | 35篇 |
1984年 | 24篇 |
1983年 | 14篇 |
1982年 | 24篇 |
1981年 | 41篇 |
1980年 | 16篇 |
1979年 | 17篇 |
1978年 | 19篇 |
1977年 | 13篇 |
1976年 | 11篇 |
1974年 | 10篇 |
1973年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
151.
152.
Alkynyl-substituted indene was first used as a ligand for the synthesis of transition metal complexes. ansa-Zirconocenes containing ethylene and dimethylsilylene bridges were synthesized starting from 2-(phenylethynyl)-1H-indene. The structure of the former compound was established by X-ray diffraction.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 68–73, January, 2007. 相似文献
153.
合成和鉴定了二安替比林基-(3-羟基)苯基甲烷(DAmHM),研究了它与V(v)的显色反应。在磷酸介质中,在Mn(Ⅱ)和吐温-40存在下,DAmHM与V(V)生成橙黄色化合物,λ_(max)=480nm,ε=1.03×10 ̄6L·mol ̄(-1)·cm ̄(-1),V(v)量在0.2~1.2ug/25mL间符合比尔定律,体系灵敏度高,稳定性好,用于中草药中痕量钒的测定,结果满意。 相似文献
154.
Summary The capillary gas chromatographic retention behavior of -pinene and tricyclene has been investigated on stationary phases of different polarities. On all but one of the columns employed, tricyclene eluted before -pinene; only permethylated -cyclodextrins dissolved in moderately polar polisiloxanes gave a reversed elution order. The intermolecular interactions which caused the unexpected retention behavior were investigated in detail, applying methods of computer simulation. To achieve this, we have developed a calculation algorithm on the basis of molecular mechanical optimizations and programmed it in a macro. This makes it possible to systematically investigate a given configuration space in which all the possible interactions can take place. It was shown that permethylated -cyclodextrin as host molecule for both guest molecules offers an optimum cavity size. As a result the number of energetically favorable contacts between host and guest molecules as well as the strength of the interactions in this stationary phase were larger. As a consequence the elution order, normally only influenced by the vapor pressure of the compounds at a given temperature, was changed. Nonspecific interactions played an especially important role for these kinds of substances. 相似文献
155.
首次研究了碳化钨负载S2 O2 -8 ZrO2 (PSZ)固体超强酸催化剂 (WC PSZ)上正戊烷的反应情况及影响催化剂活性的各种因素 ,并用GC MS ,XRD ,BET等手段分析了正戊烷反应产物和催化剂的物理化学性质等 .结果表明 :WC PSZ对正戊烷具有异构化和裂解的双重催化作用 .PSZ在负载适量碳化钨后对正戊烷反应的活性和选择性显著提高 ,显示出优于Pt PSZ催化剂的效果 ,碳化钨的负载量为 2 0 %的效果最佳 .适当的焙烧、活化和反应温度等条件是取得良好反应效果的关键 相似文献
156.
157.
Vijay Singh 《Tetrahedron letters》2006,47(39):7043-7045
Tributyltin hydride-mediated straightforward synthesis of a new isoxazolo-benzazulene system from the derivatives afforded by the Baylis-Hillman reaction of 3-(2-bromophenyl)-4-isoxazolecarbaldehydes is described. 相似文献
158.
A. Yu. Fedorov J. -P. Finet O. G. Ganina M. I. Naumov A. S. Shavyrin 《Russian Chemical Bulletin》2005,54(11):2602-2611
Benzopyran derivatives were synthesized in good yields by the reactions of tris[2-(chloromethyl)phenyl]bismuth diacetate and
2-(halomethyl)aryllead triacetates with phenols and naturally occurring 4-hydroxycoumarins in the presence of bases according
to a three-step one-pot procedure.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2520–2529, November, 2005. 相似文献
159.
Reaction of 2-(vinyloxy)ethylisothiocyanate with unsaturated carbanions generated in situ from propargyl ethers and amines when treated with superbases, after S-alkylation and cyclization of the adducts in the presence of CuBr, leads to the previously unknown 2,3,5-substituted 1-[2-(vinyloxy)ethyl]pyrroles. 相似文献
160.
Reactions of 3-(ω-haloalkoxy)-2-hydroxypropyl sulfamates with amines or ammonia followed by acid hydrolysis give the corresponding
diaminohydroxyethers.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1663–1665, August, 1998. 相似文献