全文获取类型
收费全文 | 20810篇 |
免费 | 3601篇 |
国内免费 | 3619篇 |
专业分类
化学 | 16567篇 |
晶体学 | 397篇 |
力学 | 1005篇 |
综合类 | 251篇 |
数学 | 2223篇 |
物理学 | 7587篇 |
出版年
2024年 | 60篇 |
2023年 | 413篇 |
2022年 | 681篇 |
2021年 | 823篇 |
2020年 | 902篇 |
2019年 | 1050篇 |
2018年 | 813篇 |
2017年 | 804篇 |
2016年 | 997篇 |
2015年 | 1105篇 |
2014年 | 1334篇 |
2013年 | 1627篇 |
2012年 | 1876篇 |
2011年 | 1893篇 |
2010年 | 1524篇 |
2009年 | 1435篇 |
2008年 | 1501篇 |
2007年 | 1297篇 |
2006年 | 1228篇 |
2005年 | 1054篇 |
2004年 | 904篇 |
2003年 | 726篇 |
2002年 | 730篇 |
2001年 | 647篇 |
2000年 | 440篇 |
1999年 | 387篇 |
1998年 | 264篇 |
1997年 | 186篇 |
1996年 | 229篇 |
1995年 | 181篇 |
1994年 | 170篇 |
1993年 | 153篇 |
1992年 | 117篇 |
1991年 | 111篇 |
1990年 | 78篇 |
1989年 | 56篇 |
1988年 | 53篇 |
1987年 | 37篇 |
1986年 | 40篇 |
1985年 | 40篇 |
1984年 | 16篇 |
1983年 | 19篇 |
1982年 | 4篇 |
1981年 | 6篇 |
1980年 | 4篇 |
1979年 | 3篇 |
1971年 | 1篇 |
1959年 | 4篇 |
1957年 | 2篇 |
1936年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
A simple fabrication method for tapered capillary tip and its applications in high‐speed CE and ESI‐MS
下载免费PDF全文
![点击此处可从《Electrophoresis》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Yong‐Qiang Cheng Yuan Su Xiao‐Xia Fang Jian‐Zhang Pan Qun Fang 《Electrophoresis》2014,35(10):1484-1488
Fabrication of capillaries with tapered tips is an important technique that is required in many analytical chemistry areas, such as ESI‐MS, CE, electrochemical analysis, and microinjection. This paper describes a simple and effective grinding‐based fabrication method for capillaries with tapered tips. A novel grinding mode utilizing the combination of rotation and precession of an elastic capillary was developed, which significantly improved the controllability to the grinding process as well as the capillary tip shape. The capillary was fabricated by fixing it in an electric drill installed perpendicularly, and grind the capillary tip rotated around its own axis as well as the drill axis on sandpapers. Compared with conventional fabrication techniques for capillary tips, the present method is easy to control the capillary tip shape in routine laboratories without the requirement of expensive equipments or poisonous reagent (e.g. hydrofluoric acid (HF) solution). Various capillaries with different tip diameters and tip taper angles could be fabricated using the present method with good controllability and reproducibility. These capillaries were applied in high‐speed CE and ESI‐MS analysis to demonstrate the feasibility and potential of this fabrication method. 相似文献
992.
The NMR spin–spin scalar coupling constants (JHH's) of closely contacting, but non-bonded hydrogen atoms in a series of highly strained molecules (including a new in,in-cyclophane made specifically for this study) have been examined both experimentally and computationally. The experimental JHH's are invariably quite small (0.1–0.6 Hz), but common DFT methods with modest basis sets nearly always overestimate these values, by factors of 10–30, and even with quite large basis sets (up to cc-pVQZ) the JHH's of two of the molecules are overestimated by a factor of 10 or more. Possible reasons for these discrepancies are discussed. 相似文献
993.
Jian-Jun Tang Li Zhang Li-Ping Jiang Lei Di Yong-Ming Yan Zheng-Chao Tu Cui-Ping Yang Zhi-Li Zuo Bo Hou Hou-Lin Xia Yong-Bin Chen Yong-Xian Cheng 《Tetrahedron》2014
Polyrhachis dives is consumed as an insect food in some regions of China. In this study, new dopamine derivatives, (+)-polyrhadopamine A (1a) and (−)-polyrhadopamine A (1b), (+)-polyrhadopamine B (2a) and (−)-polyrhadopamine B (2b), and polyrhadopamines C–E (3–5), were isolated from this species. The structures and stereochemistry of these substances were assigned by using spectroscopic and computational methods. Compounds 1a, 1b, 2a, and 2b are dimeric N-acetyldopamine derivatives, 3 is a dopamine analog containing an unusual sulfone group, and 4 and 5 possess a rare benzo[d]thiazole moiety. The functions of these substances as ROCK1/2 inhibitors, neural stem cell (NSCs) proliferation stimulators, immunosuppressive, and anti-inflammatory agents were determined. 相似文献
994.
Shi-Ji Xiao Xin-Xiang Lei Bing Xia Dan-Qing Xu Hong-Ping Xiao Hong-Xi Xu Fang Chen Li-Sheng Ding Yan Zhou 《Tetrahedron letters》2014
Two novel lignans, gymnothespirolignans A (1) and B (2), possessing a rare polycyclic spiro skeleton, were isolated from the endemic plant of Gymnotheca involucrata Pei. Their structures were determined by spectroscopic evidences and the absolute configurations were confirmed by single crystal X-ray diffraction analysis. Compounds 1 and 2 showed promising antiviral activities against RSV with an IC50 value of 31.87 and 17.51 μM, respectively. 相似文献
995.
Valence state parameters of all transition metal atoms in metalloproteins—development of ABEEMσπ fluctuating charge force field
下载免费PDF全文
![点击此处可从《Journal of computational chemistry》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Zhong‐Zhi Yang Jian‐Jiang Wang Dong‐Xia Zhao 《Journal of computational chemistry》2014,35(23):1690-1706
To promote accuracy of the atom‐bond electronegativity equalization method (ABEEMσπ) fluctuating charge polarizable force fields, and extend it to include all transition metal atoms, a new parameter, the reference charge is set up in the expression of the total energy potential function. We select over 700 model molecules most of which model metalloprotein molecules that come from Protein Data Bank. We set reference charges for different apparent valence states of transition metals and calibrate the parameters of reference charges, valence state electronegativities, and valence state hardnesses for ABEEMσπ through linear regression and least square method. These parameters can be used to calculate charge distributions of metalloproteins containing transition metal atoms (Sc‐Zn, Y‐Cd, and Lu‐Hg). Compared the results of ABEEMσπ charge distributions with those obtained by ab initio method, the quite good linear correlations of the two kinds of charge distributions are shown. The reason why the STO‐3G basis set in Mulliken population analysis for the parameter calibration is specially explained in detail. Furthermore, ABEEMσπ method can also quickly and quite accurately calculate dipole moments of molecules. Molecular dynamics optimizations of five metalloproteins as the examples show that their structures obtained by ABEEMσπ fluctuating charge polarizable force field are very close to the structures optimized by the ab initio MP2/6–311G method. This means that the ABEEMσπ/MM can now be applied to molecular dynamics simulations of systems that contain metalloproteins with good accuracy. © 2014 Wiley Periodicals, Inc. 相似文献
996.
Uniform cadmium sulfide (CdS) nanospheres were successfully prepared in the presence of the anionic surfactant sodium dodecylsulfate (SDS) at an appropriate concentration and relatively low temperature. Zeta potential data were collected for the three kinds of CdS particles to verify the existence of the Cd2+counterion on the CdS surface and Charge reversal; this was crucial for the explanation of how the anionic SDS surfactant molecules adsorbed on the negatively charged surface. Moreover, we confirmed that SDS had coated the surface of CdS nanospheres using infrared spectroscopy, and thermogravimetric analysis. An counterion assisted mechanism accounting for synthesis of CdS nanospheres could be widely used in the synthesis of nanomaterials if there is specific adsorption of the counterion. The CdS nanospheres showed good performance for the rapid adsorption of methylene blue. 相似文献
997.
Xin Yang R. G. Downing Guan-bo Wang Da-zhi Qian Han-gang Liu Kan Wang 《Journal of Radioanalytical and Nuclear Chemistry》2014,301(1):213-220
This paper presents a Monte Carlo code to get response spectrum of ions for the Neutron Depth Profiling (NDP) technique called Monte Carlo NDP (MC-NDP) that simulates the behavior of ions transmitted through a sample matrix and generates the energy spectrum for a specified detector. The MC-NDP model is based on the Ziegler–Biersack–Littmark Model, but incorporates the advantages of TRIM and CORTEO. The Impulse Approximation method is used to determine the flight length with the indexical interpolation method rather than the Magic algorithm for the scattering angle between ions and nucleus. This makes MC-NDP more efficient and convenient to simulate entire ion histories by a Monte Carlo approach. MC-NDP’s results agree well with both TRIM results and the experimental data. 相似文献
998.
合成了2个新配体4-(4-硫代乙酸)甲苯基-6-苯基-2,2’-联吡啶HC^N^N(PhCH2SCOCH3)(L3)和6-(4-硫代乙酸)甲苯基-2,2’-联吡啶HC^N^N(CH2SCOCH3)(L5)及其发光的铂(Ⅱ)配合物ClPtC^N^N(PhCH2SCOCH3)(C3)和ClPtC^N^N(CH2SCOCH3)(C5).通过1H NMR谱和质谱对它们的结构进行了表征,采用X射线单晶衍射分析确定了C3的晶体结构.利用紫外-可见吸收光谱、发射光谱及激发态寿命测定研究了它们的光物理性质和电化学性质,以及配合物作为光敏剂在光催化制氢中的应用.通过系列配合物产氢效率的比较,揭示了它们的产氢效率和激发态寿命的关系. 相似文献
999.
以爆炸条件下溶菌酶的反应产物为研究对象,运用基质辅助激光解吸-飞行时间质谱的方法研究其反应产物与不同炸药的反应特征性.结果显示,雷管的使用不会对溶菌酶有影响,而在有爆炸物爆炸的条件下,除了正常溶菌酶酶解多肽信号外,一些[MH+17]+,[MH+18]+,[MH+28]+,[MH+32]+和[MH+44]+的加合峰信号也能被检测到.这可能是在炸药爆炸过程中产生的一些活性小分子(如NH3,H2O,CO/N2,O2,CO2)与溶菌酶发生反应得到的反应产物.不同炸药生成的活性小分子能够分别与溶菌酶的某些反应位点反应生成特征性的反应产物,有利于这些炸药的分析与检测. 相似文献
1000.