全文获取类型
收费全文 | 9094篇 |
免费 | 161篇 |
国内免费 | 55篇 |
专业分类
化学 | 3370篇 |
晶体学 | 230篇 |
力学 | 719篇 |
综合类 | 1篇 |
数学 | 999篇 |
物理学 | 3991篇 |
出版年
2023年 | 39篇 |
2022年 | 109篇 |
2021年 | 103篇 |
2020年 | 79篇 |
2019年 | 105篇 |
2018年 | 137篇 |
2017年 | 100篇 |
2016年 | 163篇 |
2015年 | 124篇 |
2014年 | 225篇 |
2013年 | 396篇 |
2012年 | 564篇 |
2011年 | 667篇 |
2010年 | 528篇 |
2009年 | 524篇 |
2008年 | 539篇 |
2007年 | 482篇 |
2006年 | 503篇 |
2005年 | 360篇 |
2004年 | 343篇 |
2003年 | 279篇 |
2002年 | 230篇 |
2001年 | 442篇 |
2000年 | 357篇 |
1999年 | 236篇 |
1998年 | 182篇 |
1997年 | 161篇 |
1996年 | 166篇 |
1995年 | 127篇 |
1994年 | 116篇 |
1993年 | 82篇 |
1992年 | 92篇 |
1991年 | 99篇 |
1990年 | 87篇 |
1989年 | 71篇 |
1988年 | 53篇 |
1987年 | 36篇 |
1986年 | 32篇 |
1985年 | 42篇 |
1984年 | 35篇 |
1983年 | 21篇 |
1982年 | 31篇 |
1981年 | 30篇 |
1980年 | 25篇 |
1979年 | 20篇 |
1978年 | 25篇 |
1977年 | 19篇 |
1976年 | 18篇 |
1975年 | 19篇 |
1974年 | 16篇 |
排序方式: 共有9310条查询结果,搜索用时 15 毫秒
111.
G. J. Q. van der Peyl K. Isa J. Haverkamp P. G. Kistemaker 《Journal of mass spectrometry : JMS》1981,16(9):416-420
The desorption of neutrals, alkali ions and quasimolecular ions of sucrose was studied as function of substrate temperature in laser desorption mass spectrometry. These phenomena were also investigated in thermal desorption experiments. It was concluded that in these experiments gas phase cationization is the major ionization process. 相似文献
112.
Chowdhury Wasimul Q. Idehara Kenji Maeda Isamu Umeda Fusako Yagi Kiyohito Miura Yoshiharu Mizoguchi Tadashi 《Applied biochemistry and biotechnology》1996,57(1):361-366
Applied Biochemistry and Biotechnology - A marine photosynthetic bacterium,Rhodopseudomonas sp. strain W-1S, accumulated polyhydroxybutyrate (PHB) to 56% of the dry cell weight under microaerobic... 相似文献
113.
114.
The goal of in situ modification of DNA via phosphodiester alkylation has led to our design of quinone methide derivatives capable of alkylating dialkyl phosphates. A series of catechol derivatives were investigated to trap the phosphodiester-quinone methide alkylation adduct through in situ lactonization. The catechol derivatives were uniquely capable of characterizable p-quinone methide formation for mechanistic clarity. These investigations revealed that with a highly reactive lactonization group (phenyl ester), lactonization competed with quinone methide formation. Lactone-forming groups of lower reactivity (methyl ester, n-propyl ester, and dimethyl amide) allowed quinone methide formation followed by phosphodiester alkylation; however, they were ineffective at in situ lactonization to drain the phosphodiester alkylation equilibrium to the desired phosphotriester product. The derivatives tethered with lactone-forming functionality of intermediate reactivity (chloro-, trichloro-, and trifluoroethyl esters), allowed quinone methide formation, phosphodiester alkylation, and in situ lactonization to efficiently afford the trapped phosphotriester adduct. 相似文献
115.
H. Sh. Bai H. X. Jin H. Q. Fan J. Du F. Wang D. M. Chen Zh. Cheng 《Journal of Radioanalytical and Nuclear Chemistry》1998,236(1-2):87-95
The behavior of153Sm-EDTMP in vitro and vivo is analyzed by the size exclusion HPLC. The experimental results show that EDTMP amounts have an
obvious effect on the stability in vitro and uptake of153Sm-EDTMP in the liver. HPLC analysis of urine sample indicates that153Sm-EDTMP es excreted in the original form. The behavior in vivo of153Sm-EDTMP containing 4 μg is similar to that of153Sm-EDTMP containing 50 μg EDTMP at 1 h post-injection. 相似文献
116.
Capillary zone electrophoresis was employed for the determination of myoglobin in human urine using end-column amperometric detection with a carbon fiber microelectrode at a constant potential of 1.80 V vs. saturated calomel electrode (SCF). The optimum conditions of separation and detection are: 3.73 x 10-4 mol/L sodium diethyl malonyl urea (barbitone sodium), 1.34 x 10-4 mol/L HCl for the buffer solution, 20 kV for separation voltage, 5 kV and 5 s for injection voltage and injection time, respectively. The limit of detection is 4.4 x 10-8 mol/L or 84 amole signal to noise (S/N = 2). The relative standard deviation is 2.9% for the migration time and 2.5% for the electrophoretic peak current. The method can be used for the determination of myoglobin in human urine. The samples can be directly injected and need no pretreatment. The method is also rapid, less than 2 min, and has a recovery rate of 94-106%. 相似文献
117.
We extend our method of systematic removal of secular terms in a singular perturbation treatment of the Boltzmann equation with small Knudsen numbers to the initial layer. The requirement that the solution through the initial layer should connect smoothly to the normal solution removes an ambiguity noted in our previous paper. We show that removal of secular terms improves Grad's solution for the initial layer and reintroduces soundlike modes associated with higher moments, first found by Wang Chang and Uhlenbeck. 相似文献
118.
Ch. V. Subba Reddy Y. Y. Qi W. Jin Q. Y. Zhu Z. R. Deng W. Chen Sun-il Mho 《Journal of Solid State Electrochemistry》2007,11(9):1239-1243
Molybdenum trioxide (MoO3) xerogel films modified with poly(vinyl alcohol)+poly(vinyl pyrrolidone) (PVP+PVA) polyblends were obtained by ion-exchange
method with sol-gel technique. Investigations were conducted using X-ray “diffractometry”, Fourier transform infrared spectroscopy,
and cyclic voltammetry. The results show that the H atoms in polyblend are H-bonded with the O atoms in the Mo=O bonds of
MoO3 xerogel, which effectively shield the electrostatic interaction between MoO3 interlayer and Li+ ions when MoO3 xerogel is modified by the intercalation of (PVP+PVA). The reversibility of the insertion/extraction of Li+ ions is greatly improved by the modification with polyblend of MoO3 nanocomposite films. MoO3 and (PVP+PVA)
x
MoO3 (x = 0, 0.5) nanobelts were obtained by a simple hydrothermal process from MoO3 sol. The electrochemical cells with configuration Li/(LiPF6+EC+DMC)/MoO3 modified by (PVP+PVA) were fabricated and their discharge profiles studied. 相似文献
119.
Lin CS Zhang RQ Lee ST Elstner M Frauenheim T Wan LJ 《The journal of physical chemistry. B》2005,109(29):14183-14188
The assembly of small water clusters (H2O)n, n = 1-6, on a graphite surface is studied using a density functional tight-binding method complemented with an empirical van der Waals force correction, with confirmation using second-order M?ller-Plesset perturbation theory. It is shown that the optimized geometry of the water hexamer may change its original structure to an isoenergy one when interacting with a graphite surface in some specific orientation, while the smaller water cluster will maintain its cyclic or linear configurations (for the water dimer). The binding energy of water clusters interacting with graphite is dependent on the number of water molecules that form hydrogen bonds, but is independent of the water cluster size. These physically adsorbed water clusters show little change in their IR peak position and leave an almost perfect graphite surface. 相似文献
120.
This is the first report on the determination of proteins with tetra-substituted sulphonated aluminum phthalocyanine (AlS4Pc) by resonance light-scattering (RLS). At pH 3.0, the weak RLS of AlS4Pc can be enhanced by the addition of proteins. Based on this, a novel quantitative method has been developed for the determination of proteins in aqueous solutions. Under optimal conditions, the linear ranges of the calibration curves were 0.050–2.0 μg ml−1 for both human serum albumin (HSA) and human r-IgG. The detection limits were 12.7 ng ml−1 for HSA and 16.1 ng ml−1 for human r-IgG. The method has been applied to the analysis of total protein in human serum samples collected from the hospital and the results were in good agreement with those reported by the hospital, which indicates that the method presented here is not only sensitive, simple, but also reliable and suitable for practical applications. 相似文献