全文获取类型
收费全文 | 8982篇 |
免费 | 1711篇 |
国内免费 | 965篇 |
专业分类
化学 | 6050篇 |
晶体学 | 86篇 |
力学 | 730篇 |
综合类 | 65篇 |
数学 | 1132篇 |
物理学 | 3595篇 |
出版年
2024年 | 38篇 |
2023年 | 189篇 |
2022年 | 308篇 |
2021年 | 325篇 |
2020年 | 353篇 |
2019年 | 324篇 |
2018年 | 296篇 |
2017年 | 296篇 |
2016年 | 435篇 |
2015年 | 426篇 |
2014年 | 473篇 |
2013年 | 653篇 |
2012年 | 763篇 |
2011年 | 845篇 |
2010年 | 562篇 |
2009年 | 535篇 |
2008年 | 634篇 |
2007年 | 490篇 |
2006年 | 523篇 |
2005年 | 391篇 |
2004年 | 327篇 |
2003年 | 259篇 |
2002年 | 237篇 |
2001年 | 202篇 |
2000年 | 193篇 |
1999年 | 194篇 |
1998年 | 182篇 |
1997年 | 173篇 |
1996年 | 169篇 |
1995年 | 137篇 |
1994年 | 121篇 |
1993年 | 112篇 |
1992年 | 91篇 |
1991年 | 69篇 |
1990年 | 75篇 |
1989年 | 61篇 |
1988年 | 45篇 |
1987年 | 34篇 |
1986年 | 34篇 |
1985年 | 22篇 |
1984年 | 18篇 |
1983年 | 14篇 |
1982年 | 15篇 |
1981年 | 3篇 |
1980年 | 7篇 |
1979年 | 2篇 |
1975年 | 1篇 |
1957年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
141.
Spin preference and S-T gaps of localized 1,3-diradicals were studied by an orbital phase theory and theoretical calculations. The orbital phase theory was applied to rationalize thermodynamic and kinetic stabilities of diradicals. We theoretically designed some singlet localized 1,3-diradicals, substituted trimethylenes, which are more stable than the lowest triplets. Some diradicals with the four-membered rings, 2,4-disilacyclobutane-1,3-diyls, were designed and shown to have singlet ground states and to be more stable than the sigma-bonded isomers, 2,4-disilabicyclo[1.1.0]butanes. The ab initio calculations supported predictions of the stable carbon-centered localized singlet 1,3-diradicals. 相似文献
142.
143.
Insulating tubular BN sheathing on semiconducting nanowires 总被引:1,自引:0,他引:1
Zhu YC Bando Y Xue DF Xu FF Golberg D 《Journal of the American Chemical Society》2003,125(47):14226-14227
An effective method was developed for generation of insulating tubular boron nitride (BN)-sheathed nanostructures. ZnS nanowires and multilayered Si-SiO2 nanowires were successfully sheathed with insulating tubular BN-forming nanocables. Both the semiconductor nanowire cores and the BN sheaths are crystalline with well-uniform morphologies. 相似文献
144.
Yubin Xue Shun‐Chang Liu Xinsheng Liu Yusi Yang Yimin Zhang Ding‐Jiang Xue Jin‐Song Hu 《中国化学》2020,38(4):356-360
Colloidal quantum dots (CQDs) are attractive absorber materials for high‐efficiency photovoltaics because of their facile solution processing, bandgap tunability due to quantum confinement effect, and multi‐exciton generation. To date, all published performance records for PbS CQDs solar cells have been based on the conventional hot‐injection synthesis method. This method usually requires relatively strict conditions such as high temperature and the utility of expensive source material (pyrophoric bis(trimethylsilyl) sulfide (TMS‐S)), limiting the potential for large‐scale and low‐cost synthesis of PbS CQDs. Here we report a facile room‐temperature synthetic method to produce high‐quality PbS CQDs through inexpensive ionic source materials including Pb(NO3)2 and Na2S in the presence of triethanolamine (TEA) as the stabilizing ligand. The PbS CQDs were successfully prepared with an average particle size of about 5 nm. Solar cells based on the as‐synthesized PbS CQDs show a preliminary power conversion efficiency of 1.82%. This room‐temperature and low‐cost synthesis of PbS CQDs will further benefit the development of solution‐processed CQD solar cells. 相似文献
145.
Cheng-Ting Zi Liu Yang Fa-Wu Dong Qing-Hua Kong Zhong-Tao Ding Jun Zhou 《Natural product research》2020,34(16):2301-2309
Abstract Two new compounds (9 and 10) having a camptothecin (CPT) analog conjugated to the 4β-azido-4-deoxypodophyllotixin analog by untilizing the copper-catalyzed azide-alkyne cycloadditon (CuAAC) reaction, and were evaluated for their cytotoxicity against a panel of five human cancer cell lines (HL-60, SMMC-7721, A-549, MCF-7 and SW480) using the MTT (3-(4,5-dimethyl-thiahiazo-2-yl)-2,5-diphenyltetrazolium bromide) assay. Two novel conjugates shown weak cytotoxicity, compound 10 showed highly potent against HL-60 cell line tested, with IC50 value 17.69?±?0.19?μM. This compound suggested its potential as anticancer agents for further development. 相似文献
146.
Yiyi Weng Xingxing Ding Joo C. A. Oliveira Xiaobin Xu Nikolaos Kaplaneris Meijie Zhu Hantao Chen Zhuo Chen Lutz Ackermann 《Chemical science》2020,11(34):9290
There is a strong demand for novel native peptide motifs for post-synthetic modifications of peptides without pre-installation and subsequent removal of directing groups. Herein, we report an efficient method for peptide late-stage C(sp3)–H arylations assisted by the unmodified side chain of asparagine (Asn) without any exogenous directing group. Thereby, site-selective arylations of C(sp3)–H bonds at the N-terminus of di-, tri-, and tetrapeptides have been achieved. Likewise, we have constructed a key building block for accessing agouti-related protein (AGRP) active loop analogues in a concise manner.An efficient method for peptide late-stage C(sp3)-H arylations assisted by unmodified side chain of asparagine (Asn) without any exogenous directing group has been reported. 相似文献
147.
[reaction: see text] A microwave-assisted reaction was developed to facilitate the construction of 4,5-disubstituted pyrazolopyrimidines. This one-pot two-step process involves a sequential S(N)Ar displacement of the C4 chloro substituent with various anilines and amines, followed by a Suzuki coupling reaction with different boronic acids. Using microwave irradiation leads to high product conversion, low side product formation, and shorter reactions. 相似文献
148.
Microdialysis sampling coupled to HPLC for transdermal delivery study of ondansetron hydrochloride in rats 总被引:3,自引:0,他引:3
The transdermal delivery of ondansetron hydrochloride (ON) solution in propylene glycol (PG) with a widely used penetration enhancer, oleic acid (OA), was studied in rats by a microdialysis sampling technique. Dialysate samples collected from the probe were directly injected into the HPLC system without any pre-treatment and no interference occurred in the blank sample. A good linearity between the standard concentrations and peak areas within the calibration range was achieved. In vivo recovery (32.52 +/- 1.8%) of the probe was assessed with the retrodialysis method, which was used to calculate the ON concentration in the dermis. Oleic acid at the concentrations of 2% and 5% (w/v) increased the steady-state delivery rate from 0.001 to 0.030 and 0.058 microg/h, respectively. OA proved to be an effective enhancer for transdermal delivery of ON in rats. 相似文献
149.
150.