全文获取类型
收费全文 | 62500篇 |
免费 | 10956篇 |
国内免费 | 8909篇 |
专业分类
化学 | 45652篇 |
晶体学 | 949篇 |
力学 | 3705篇 |
综合类 | 679篇 |
数学 | 7079篇 |
物理学 | 24301篇 |
出版年
2024年 | 228篇 |
2023年 | 1252篇 |
2022年 | 2195篇 |
2021年 | 2214篇 |
2020年 | 2510篇 |
2019年 | 2550篇 |
2018年 | 2228篇 |
2017年 | 2125篇 |
2016年 | 3027篇 |
2015年 | 3103篇 |
2014年 | 3657篇 |
2013年 | 4623篇 |
2012年 | 5394篇 |
2011年 | 5570篇 |
2010年 | 4015篇 |
2009年 | 3918篇 |
2008年 | 4203篇 |
2007年 | 3721篇 |
2006年 | 3651篇 |
2005年 | 3003篇 |
2004年 | 2427篇 |
2003年 | 2066篇 |
2002年 | 2073篇 |
2001年 | 1678篇 |
2000年 | 1540篇 |
1999年 | 1346篇 |
1998年 | 1063篇 |
1997年 | 929篇 |
1996年 | 962篇 |
1995年 | 823篇 |
1994年 | 748篇 |
1993年 | 606篇 |
1992年 | 550篇 |
1991年 | 447篇 |
1990年 | 381篇 |
1989年 | 305篇 |
1988年 | 248篇 |
1987年 | 212篇 |
1986年 | 197篇 |
1985年 | 186篇 |
1984年 | 119篇 |
1983年 | 89篇 |
1982年 | 65篇 |
1981年 | 43篇 |
1980年 | 22篇 |
1979年 | 14篇 |
1973年 | 4篇 |
1959年 | 5篇 |
1957年 | 9篇 |
1936年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
993.
To obtain new materials with synergetic or complementary behaviors, polyaniline composite filled with ZnO rods in ramification-like
structure was prepared by a hydrothermal approach. Comparative experiments of ZnO preparation in the presence of some metal
ions were also carried out. The results indicated that the morphology of ZnO was strongly affected by the preparation condition.
The method to grow ZnO rods in the presence of polyaniline offers a simple approach to obtain polyaniline composite filled
with linear ZnO structure. The results of X-ray photoelectron spectroscopy show that the strong interaction between ZnO and
polyaniline possibly exists to cause the charge transfer. 相似文献
994.
The fluorimetric determination of mercury ions with o-vanillin-8-aminoquinoline (OVAQ) in aqueous solutions was investigated. Hg(II) could react with the fluorescent reagent OVAQ
(λex/em = 278/314 nm) to form a nonfluorescent complex in an ethanol-water medium of pH 6.00. The linear range of the proposed method
was from 2.5 to 80 μg/L, and the detection limit was 0.80 μg/L. The interferences of 24 foreign ions were also studied. The
method was successfully applied to the determination of Hg(II) in sludge.
The text was submitted by the authors in English. 相似文献
995.
Y. Xu B. Conway J. S. G. Montaner M. V. O'Shaughnessy C. L. Greenstock 《Photochemistry and photobiology》1996,64(2):238-241
Recent studies have demonstrated that UV light and x-irradiation enhance human immunodeficiency virus (HIV) gene expression. There are few published data on related effects of γ-radiation. This may be of clinical relevance, as radiotherapy has been used extensively for the treatment of acquired immunodeficiency syndrome associated conditions. With this in mind, we have studied the effects of γ-radiation on HIV replication in mononuclear cells (MC). These cells were obtained from five seronegative healthy donors, exposed to0–200 cGy γ-radiation, stimulated with phytohemagglutinin-P (PHA-P) for 24 h, infected with a laboratory strain of HIV (HTLV-IIIB, multiplicity of infection = 0.001), then carried in culture for 14 days. Overall, when considering p24 antigen levels on days 7 and 11 in cultures established from cells exposed to 50 cGy, the maximal levels were significantly higher than those measured in the parallel control cultures taken as a whole (P < 0.05), with viral replication enhanced as much as 1000-fold in one case. No significant cytotoxicity was observed following exposure to doses up to 50 cGy. The mechanism of the observed effect remains unknown but may relate to direct gene activation and/or free radical generation, leading to such activation. To date, there is no evidence that viral stimulation occurs following therapeutic radiation in a clinical setting. 相似文献
996.
Yang HH Zhang SQ Yang W Chen XL Zhuang ZX Xu JG Wang XR 《Journal of the American Chemical Society》2004,126(13):4054-4055
In this study, we report a simple procedure for applying molecular imprinting functional groups to the inner surfaces of the template-synthesized sol-gel nanotubes for chemical separation of estrone. The silica nanotubes were synthesized within the pores of nanopore alumina template membranes using a sol-gel method by simultaneous hydrolysis of a silica monomer-imprinted molecule complex and tetraethoxysilane (TEOS). A covalent imprinting strategy was employed by generating a sacrificial spacer through the reaction of the isocyanate group of 3-(triethoxysilyl)propyl isocyanate and a phenol moiety of estrone to form a thermally cleavable urethane bond. This allowed us to remove the imprinted estrone by simple thermal reaction and to simultaneously introduce functional groups into the cavity formed by the silica nanotubes. Experiments indicated that estrone could be bound selectively by such an approach and have a binding affinity of 864 +/- 137 (n = 3). 相似文献
997.
Sesquiterpene esters from the fruits of Celastrus orbiculatus 总被引:1,自引:0,他引:1
Three new beta-dihydroagarofuran sesquiterpene esters, 6 alpha-acetoxy-9 beta-benzoyloxy-1 beta-cinnamoyloxy-8 beta-butanoyloxy-beta-dihydroagarofuran (1), 6 alpha-acetoxy-9 beta-benzoyloxy-1 beta-cinnamoyloxy-8 beta-(2-methylbutanoyloxy)-beta-dihydroagarofuran (2), and 6 alpha-acetoxy-1 beta,8 beta-dibenzoyloxy-9 beta-hydroxy-beta-dihydroagarofuran (6), together with three known compounds (3-5) were isolated from the fruits of Celastrus orbiculatus THUNB. Their structures were elucidated on the basis of spectroscopic methods. Compound 4 showed moderate activity in inhibiting LPS-induced nitric oxide production in murine macrophage RAW264.7 cells with an IC(50) value of 43.7 microM. 相似文献
998.
A new series of thiophene‐ and furan‐containing chromophores with a chiral prolinol donor and a sulfone acceptor has been synthesized. The UV‐vis absorptions, second‐order nonlinear optical properties, and X‐ray crystal structures are described. 相似文献
999.
Qiongyou Wu Fanqi Qu Jinqiao Wan Xun Zhu Yi Xia Ling Peng 《Helvetica chimica acta》2004,87(4):811-819
Ribavirin, the only small molecule available so far for treating hepatitis‐C‐virus infection, was recently used in an emergency context to treat patients with severe acute respiratory syndrome (SARS) in the early stages of the disease. To study the mechanisms responsible for the antiviral effects of ribavirin by using a photolabeling approach, we designed, synthesized, and characterized the azidotriazole nucleosides 1 and 2 as photolabeling probes of ribavirin. These probes were synthesized either by performing nucleophilic substitution of the corresponding bromotriazole nucleoside with NaN3 (Scheme 2) or by directly coupling the azidotriazole with the protected ribose sugar (Scheme 4). The azidotriazole nucleosides 1 and 2 showed a fast, clear‐cut photochemical reaction, which suggests that they are promising candidates for use in photolabeling studies. 相似文献
1000.