全文获取类型
收费全文 | 12551篇 |
免费 | 330篇 |
国内免费 | 26篇 |
专业分类
化学 | 7664篇 |
晶体学 | 183篇 |
力学 | 329篇 |
数学 | 1113篇 |
物理学 | 3618篇 |
出版年
2023年 | 114篇 |
2022年 | 234篇 |
2021年 | 195篇 |
2020年 | 220篇 |
2019年 | 283篇 |
2018年 | 251篇 |
2017年 | 287篇 |
2016年 | 426篇 |
2015年 | 284篇 |
2014年 | 516篇 |
2013年 | 975篇 |
2012年 | 746篇 |
2011年 | 876篇 |
2010年 | 548篇 |
2009年 | 523篇 |
2008年 | 610篇 |
2007年 | 571篇 |
2006年 | 435篇 |
2005年 | 423篇 |
2004年 | 326篇 |
2003年 | 269篇 |
2002年 | 263篇 |
2001年 | 141篇 |
2000年 | 154篇 |
1999年 | 107篇 |
1998年 | 84篇 |
1997年 | 85篇 |
1996年 | 114篇 |
1995年 | 115篇 |
1994年 | 117篇 |
1993年 | 117篇 |
1992年 | 135篇 |
1991年 | 101篇 |
1990年 | 94篇 |
1989年 | 111篇 |
1988年 | 106篇 |
1987年 | 103篇 |
1986年 | 89篇 |
1985年 | 119篇 |
1984年 | 143篇 |
1983年 | 96篇 |
1982年 | 114篇 |
1981年 | 110篇 |
1980年 | 118篇 |
1979年 | 104篇 |
1978年 | 120篇 |
1977年 | 108篇 |
1976年 | 67篇 |
1975年 | 75篇 |
1974年 | 86篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
21.
22.
The output characteristics of a high repetition rate pulsed dye laser has both short-term fluctuations and long-term drift.
In high power high repetition rate lasers flow induced variations dominate over those due to other factors. In this paper
it is shown by dye laser measurements that bandwidth fluctuations can be traced to the effective changes of the resonator
dispersion due to fluctuations in the penetration depth of the pump beam in the dye medium. Short-term wavelength fluctuations
can be traced to instantaneous deflection of the dye laser axis by the refractive index changes due to absorption of the pump
beam. The fluctuations in both the bandwidth and the wavelength decreases with increasing flow rates within a laminar region.
A copper vapor laser operating at 5.6 kHz repetition rate pumped the Rhodamine 6G dye laser used. The wavelength fluctuation
of ±0.0035, 0.0030, 0.0004 nm and the bandwidth fluctuation of ±710, 132, 45 MHz over approx. 60 minutes were observed at
1.2, 3.7, 5.5 lpm flow rates respectively. 相似文献
23.
The elastic constants of dilute alloys based on bcc metals have been calculated using the Green’s function method obtaining
explicit expressions for change in elastic constants in terms oft-matrix. The crystal impurity problem is discussed within an impurity model containing central and non-central force constant
changes extended up to second neighbours of the impurity. The effect of volume change on elastic constants and a contribution
from electron pressure term are considered. Numerical results for changes in three elastic moduli have been presented for
a number of dilute alloys based on Mo, Nb, W, Ta and V. 相似文献
24.
25.
Ram K. Ganesh 《国际流体数值方法杂志》1991,13(5):557-578
The total drag force on the surface of a body, which is the sum of the form drag and the skin friction drag in a 2D domain, is numerically evaluated by integrating the energy dissipation rate in the whole domain for an incompressible Stokes fluid. The finite element method is used to calculate both the energy dissipation rate in the whole domain as well as the drag on the boundary of the body. The evaluation of the drag and the energy dissipation rate are post-processing operations which are carried out after the velocity field and the pressure field for the flow over a particular profile have been obtained. The results obtained for the flow over three different but constant area profiles—a circle, an ellipse and a cross-section of a prolate spheroid—with uniform inlet velocity are presented and it is shown that the total drag force times the velocity is equal to the total energy dissipation rate in the entire finite flow domain. Hence, by calculating the energy dissipation rate in the domain with unit velocity specified at the far-field boundary enclosing the domain, the drag force on the boundary of the body can be obtained. 相似文献
26.
Conductivity, viscosity, turbidity, and NMR measurements were performed over most of the mole fraction range for sodium deoxycholate (SDC) with hexadecyltrimethylammonium bromide (HTAB), hexadecylpyridinium bromide (HPyBr), and hexadecylpyridinium chloride (HPyCl). All studies demonstrate that the mixed-micelle formation is more favorable in SDC plus HTAB rather than SDC plus HPyBr or SDC plus HPyCl mixtures. The results showed that the bulky pyridinium head groups of HPyBr or HPyCl create steric incompatibility with rigid SDC monomers in the mixed state. 相似文献
27.
E. A. Davis A. Singh S. F. J. Cox S. R. Kreitzman T. L. Estle B. Hitti R. L. Lichti R. DuVarney 《Hyperfine Interactions》1994,86(1):705-710
Studies of the muonium fractions in the amorphous oxide a-SiO have been carried out by RF resonance at TRIUMF, Canada and LF repolarization techniques at RAL, U.K. The resonance measurements confirm the presence of the interstitial Mu centre in this intermediate oxide of silicon. Analysis of the data gathered at RAL, using a recently-developed fitting technique, reveals that the Mu* state is present here as well, but with lower relative fractions than in a-Si. However, as in the latter material, but in contrast to c-Si, this bond-centre species appears to be stable up to room temperature. 相似文献
28.
M. Singh 《Journal of the Iranian Chemical Society》2006,3(4):334-339
Using upper consolute temperatures (UCT) and corresponding consolute compositions (CC) of water-phenol systems with each of 0.1 mol kg?1 salts and acids, 1.0% polyethylene glycol 200, 0.01 mol kg?1 surfactant and aromatic compounds, we obtained 0.01 mol kg?1 CaF2 and CrCl3 compositions. Focusing on UCT and CC, the role of valence electrons and shell number, basicity, hydrophilic, hydrophobic and π conjugated electrons of corresponding additives are reported. The surfactants and π conjugation electrons are noted to decrease the UCT in a constant ratio that depicts the state and inherent strength of ionic and molecular-water interactions. The data are useful in the investigation of cloud points of immiscible solutions based on the Hofmeister series. 相似文献
29.
30.
P.Veeraraghavan Ramachandran Kamlesh J Padiya Vivek Rauniyar M.Venkat Ram Reddy Herbert C Brown 《Journal of fluorine chemistry》2004,125(4):615-620
Asymmetric “allyl”boration of pentafluorobenzaldehyde with various α-pinene based “allyl”boranes provides homoallylic alcohols in high de and ee; the alcohols have been converted into δ-lactones via acryloylation, ring-closing metathesis and hydrogenation. Pentafluorophenyl analog of key pharmacophore of statin drugs has been synthesized using diastereoselective epoxidation and regioselective reduction as key steps. 相似文献