全文获取类型
收费全文 | 347449篇 |
免费 | 3340篇 |
国内免费 | 966篇 |
专业分类
化学 | 185685篇 |
晶体学 | 6089篇 |
力学 | 14398篇 |
综合类 | 12篇 |
数学 | 37415篇 |
物理学 | 108156篇 |
出版年
2020年 | 2931篇 |
2019年 | 3244篇 |
2018年 | 3922篇 |
2017年 | 4112篇 |
2016年 | 6229篇 |
2015年 | 3802篇 |
2014年 | 6143篇 |
2013年 | 15661篇 |
2012年 | 11377篇 |
2011年 | 13734篇 |
2010年 | 9903篇 |
2009年 | 9924篇 |
2008年 | 12684篇 |
2007年 | 12495篇 |
2006年 | 11805篇 |
2005年 | 10658篇 |
2004年 | 9767篇 |
2003年 | 8920篇 |
2002年 | 8611篇 |
2001年 | 10398篇 |
2000年 | 7829篇 |
1999年 | 6022篇 |
1998年 | 4887篇 |
1997年 | 4719篇 |
1996年 | 4536篇 |
1995年 | 4226篇 |
1994年 | 4111篇 |
1993年 | 3917篇 |
1992年 | 4773篇 |
1991年 | 4622篇 |
1990年 | 4509篇 |
1989年 | 4504篇 |
1988年 | 4492篇 |
1987年 | 4514篇 |
1986年 | 4282篇 |
1985年 | 5541篇 |
1984年 | 5617篇 |
1983年 | 4624篇 |
1982年 | 4815篇 |
1981年 | 4698篇 |
1980年 | 4457篇 |
1979年 | 4923篇 |
1978年 | 4969篇 |
1977年 | 5029篇 |
1976年 | 4906篇 |
1975年 | 4577篇 |
1974年 | 4519篇 |
1973年 | 4650篇 |
1972年 | 3122篇 |
1968年 | 2787篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
201.
202.
Mutual precipitates of poly (N, N-dimethyl acrylamide) and poly (4-hydroxystyrene) were collected from dioxane, methanol, or acetone. The glass transition (Tg) temperatures of the precipitates are higher than the weight-average values. Clear films cast from dimethylformamide solutions have lower Tg values. Complexation also occurred between poly (ethyl oxazoline) and poly (4-hydroxystyrene) in dioxane and between poly (vinyl pyrrolidone) and poly (4-hydroxystyrene) in methanol. Again, the glass transition temperatures of the precipitates are higher than the values for the blend films. The ΔCp values associated with the glass transitions of the complexes are smaller than those of the blends having the same compositions. Negative excess heat capacities of mixing have been observed for several precipitates. 相似文献
203.
A E Abdel-Megied P Hansen E B Pedersen C M Nielsen 《Acta chemica Scandinavica (Copenhagen, Denmark : 1989)》1991,45(10):1060-1063
The 3'-iodonucleoside 4 and the 3'-O-methylsulfonylthymidine 9 have been synthesized by condensation of silylated uracils 2 with methyl 5-O-tert-butyldiphensilyl-2,3-dideoxy-3-iodo-D-threo-pentofuran oside (3) and methyl 5-O-tert-butyldiphenylsilyl-2-deoxy-3-methylsulfonyl-D-erythro- pentofuranoside (8), respectively. The nucleoside 4 and 9 produced the corresponding 2',3'-didehydro-2',3'-dideoxynucleosides 5 in an elimination reaction on treatment with sodium methoxide. The compounds 5b showed no antiviral activity against HIV-1. 相似文献
204.
A simple High performance liquid chromatographic (HPLC) method for the specific determination of the molecular weight and concentration of hyaluronic acid (HA) in complex mixtures has been developed. Hyaluronate-binding proteins isolated from bovine cartilage labelled by 125I or fluoresceinisothiocyanate were used as specific markers. The specific binding affinities of the markers were compared and were found to have association constants of 1.6 x 10(7) M-1 and 1.2 x 10(7) M-1 respectively. The HA levels and molecular weight distributions can be easily determined in the range 10-500 ng/mL in complex mixtures by the use of markers, molecular sieving HPLC columns and appropriate detectors. It has been demonstrated clearly that the method is useful for the highly specific determination of the parameters in complex biological samples such as serum and synovial fluids and is recommended for clinical applications. 相似文献
205.
A three-phase model of a hybrid chiral quark bag is proposed. In addition to the phases of asymptotically free current quarks
and of totally colorless mesons, the model contains the intermediate phase of massive constituent quarks. A self-consistent
solution with an account for the “Dirac sea” contribution is found in the (1+1)-dimensional case. The dependence of the bag
parameters on the parameters of the theory is investigated analytically and numerically.
Translated from Teoreticheskaya i Matematicheskaya Fizika, Vol. 117, No. 2, pp. 263–299, November, 1998. 相似文献
206.
I. G. Yudelevich B. I. Zaksas Ye. A. Petrova A. S. Cherevko 《Fresenius' Journal of Analytical Chemistry》1991,340(9):560-563
Summary A method for the atomic emission spectrometric analysis of air and water with inductively coupled and two-jet direct current plasmas has been developed. The method has been applied to the determination of impurity contents with good accuracy and sensitivity. 相似文献
207.
Unsteady flow dynamics in doubly constricted 3D vessels have been investigated under pulsatile flow conditions for a full cycle of period T. The coupled non‐linear partial differential equations governing the mass and momentum of a viscous incompressible fluid has been numerically analyzed by a time accurate Finite Volume Scheme in an implicit Euler time marching setting. Roe's flux difference splitting of non‐linear terms and the pseudo‐compressibility technique employed in the current numerical scheme makes it robust both in space and time. Computational experiments are carried out to assess the influence of Reynolds' number and the spacing between two mild constrictions on the pressure drop across the constrictions. The study reveals that the pressure drop across a series of mild constrictions can get physiologically critical and is also found to be sensitive both to the spacing between the constrictions and the oscillatory nature of the inflow profile. The flow separation zone on the downstream constriction is seen to detach from the diverging wall of the constriction leading to vortex shedding with 3D features earlier than that on the wall in the spacing between the two constrictions. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
208.
209.
On the basis of the model “polymer chain in an array of obstacles” the influence of the topology effects on the dynamics of concentrated polymer systems is investigated theoretically. The 1/z-expansion (where z is the coordinational number of the lattice of obstacles) is proposed for this problem. By means of this expansion the diffusion coefficient of a linear unclosed polymer chain is calculated. The equilibrium properties of linear closed chain (i.e. ring) unentangled with either of the edges of the lattice are investigated in detail. In particular, it is shown that the diffusion coefficient D of the center of mass of closed chain consisting of N links is proportional to N−5/2. 相似文献
210.