全文获取类型
收费全文 | 56373篇 |
免费 | 10051篇 |
国内免费 | 1516篇 |
专业分类
化学 | 54280篇 |
晶体学 | 552篇 |
力学 | 1185篇 |
数学 | 4077篇 |
物理学 | 7846篇 |
出版年
2023年 | 139篇 |
2022年 | 117篇 |
2021年 | 707篇 |
2020年 | 1619篇 |
2019年 | 2928篇 |
2018年 | 1358篇 |
2017年 | 982篇 |
2016年 | 3907篇 |
2015年 | 3975篇 |
2014年 | 4087篇 |
2013年 | 5286篇 |
2012年 | 4526篇 |
2011年 | 3946篇 |
2010年 | 3922篇 |
2009年 | 3746篇 |
2008年 | 3837篇 |
2007年 | 3037篇 |
2006年 | 2807篇 |
2005年 | 2760篇 |
2004年 | 2431篇 |
2003年 | 2148篇 |
2002年 | 2730篇 |
2001年 | 1840篇 |
2000年 | 1688篇 |
1999年 | 667篇 |
1998年 | 252篇 |
1997年 | 216篇 |
1996年 | 246篇 |
1995年 | 184篇 |
1994年 | 202篇 |
1993年 | 205篇 |
1992年 | 154篇 |
1991年 | 127篇 |
1990年 | 117篇 |
1989年 | 103篇 |
1988年 | 69篇 |
1987年 | 75篇 |
1986年 | 50篇 |
1985年 | 79篇 |
1984年 | 53篇 |
1983年 | 48篇 |
1982年 | 69篇 |
1981年 | 68篇 |
1980年 | 38篇 |
1979年 | 51篇 |
1978年 | 49篇 |
1977年 | 40篇 |
1976年 | 46篇 |
1975年 | 39篇 |
1974年 | 40篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
981.
A detailed singlet potential energy surface(PES) of [Si,C,O,O] system including a van der Waals (vdW) comples SiO……CO2,eight isomers,and twelve transiton states is investigated by MP2 and QCISD(T) (single-point)methods.At the final QCISD(T)/6-311 G(2df)//MP2/6-311G(d) level with zero-point energy included,the complex SiO……CO is found to be thermodynamically and kinetically the most stable species.Although eight ismoers are located as local energy minima,they are rather unstable toward isomerization to the dissociation fragments or comples.For the reaction of silocon atoms with carbon dioxide,two competitive reaction channels are found,and the primary pathway,which leads to the products of SiO and CO fragments,is the direct oxygen-abstraction process from carbon dioxide by silicon atom with a41.16 kJ/mol reaction barrier height.Our predications are in good agreement with previous experimental and theoretical studies. 相似文献
982.
A new trihydroxy briarane-related diterpenoid, junceellolide I (1), along with a known metabolite, (1R,2R,5Z,7R,8S,9R,10R,12R,14R,17S)-2,14-diacetoxy-8,17-epoxy-9,12-dihydroxybriara-5,11(20)-dien-19-one (2), have been isolated from the gorgonian coral Junceella fragilis, collected off the southern Taiwan coast. The structure, including the relative configuration of the new compound 1, was elucidated by the combination of spectral data, particularly in high-resolution 1H- and 13C-NMR spectroscopy utilizing COSY, HMBC, HMQC, and NOESY experiments. 相似文献
983.
984.
985.
Styrene was polymerized in the presence of benzoyl peroxide (BPO) and 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) to yield polystyrene-TEMPO (PS-TEMPO) macroinitiator. The PS-TEMPO macroinitiator with different molecular weight was reacted with 4-vinyl pyridine (4-VP) to synthesize polystyrene-block-poly(4-vinyl pyridine) (PS-b-PVP), which was then quaternized with n-octyl iodide. Antibacterial activity of the quaternized copolymers was assessed against a gram negative bacterium (Pseudomonas aeruginosa) and a gram positive one (Staphylococcus aureus) by using the shake flask test method, and the results were compared with those of poly(styrene-random-4-vinyl pyridine) (P(ST-r--VP)). The quaternized copolymers inhibited greatly the growth of the bacteria, and PS-b-PVP was more active than P(ST-r-VP), which was ascribed to the fact that the content of quaternized 4-VP units on the surface of the particles of the former copolymer was higher than that corresponding to the latter one. 相似文献
986.
987.
A piezoelectric nucleic acid sensor was constructed ofr detection of tumor necrosis factor gene.Two methods were employed for immobilization of nucleic acid probe on gold electrode of piezoelectric crystal.The results show that polyethyleneimine adbesion and glutaraldehyde cross-linking method has higher sensitivity,stability and selectivity than protein A method.The solid-phase nucleic acid hybridization of oligo unclecotides and tumor necrosis factor target gene sequence were monitorde using this sensor.Tumor necrosis factor gene sequence(580bp) was detected by this nucleic acid sensor for the first time. 相似文献
988.
Chen T Barton SC Binyamin G Gao Z Zhang Y Kim HH Heller A 《Journal of the American Chemical Society》2001,123(35):8630-8631
989.
[formula: see text] Paclitaxel and epothilone represent the two major classes of antimicrotubule agents that promote tubulin polymerization and, presumably, mitotic arrest during cell division. A common minireceptor binding site model at beta-tubulin has been constructed for these structurally divergent compounds. Utilizing 20 amino acids identified in photoaffinity labeling experiments, the 3-D model correlates measured and predicted Ki's with r = 0.99 and rms(delta Gcalc-delta Gexp) = 0.2 kcal/mol. In addition, the model predicts the affinity of compounds not used in the training set and explains much of the SAR for the paclitaxel and epothilone families. 相似文献
990.