全文获取类型
收费全文 | 6825篇 |
免费 | 218篇 |
国内免费 | 57篇 |
专业分类
化学 | 5076篇 |
晶体学 | 47篇 |
力学 | 241篇 |
综合类 | 2篇 |
数学 | 876篇 |
物理学 | 858篇 |
出版年
2024年 | 15篇 |
2023年 | 68篇 |
2022年 | 337篇 |
2021年 | 346篇 |
2020年 | 226篇 |
2019年 | 255篇 |
2018年 | 249篇 |
2017年 | 190篇 |
2016年 | 325篇 |
2015年 | 228篇 |
2014年 | 241篇 |
2013年 | 616篇 |
2012年 | 409篇 |
2011年 | 436篇 |
2010年 | 286篇 |
2009年 | 254篇 |
2008年 | 317篇 |
2007年 | 316篇 |
2006年 | 250篇 |
2005年 | 230篇 |
2004年 | 216篇 |
2003年 | 171篇 |
2002年 | 183篇 |
2001年 | 65篇 |
2000年 | 71篇 |
1999年 | 58篇 |
1998年 | 31篇 |
1997年 | 51篇 |
1996年 | 51篇 |
1995年 | 37篇 |
1994年 | 42篇 |
1993年 | 33篇 |
1992年 | 38篇 |
1991年 | 33篇 |
1990年 | 47篇 |
1989年 | 32篇 |
1988年 | 24篇 |
1987年 | 28篇 |
1986年 | 27篇 |
1985年 | 42篇 |
1984年 | 20篇 |
1983年 | 22篇 |
1982年 | 31篇 |
1981年 | 24篇 |
1980年 | 23篇 |
1979年 | 21篇 |
1978年 | 17篇 |
1977年 | 15篇 |
1976年 | 11篇 |
1975年 | 8篇 |
排序方式: 共有7100条查询结果,搜索用时 0 毫秒
1.
Inner derivations and norm equality 总被引:3,自引:0,他引:3
Mohamed Barraa Mohamed Boumazgour 《Proceedings of the American Mathematical Society》2002,130(2):471-476
We characterize when the norm of the sum of two bounded operators on a Hilbert space is equal to the sum of their norms.
2.
An admissible minimax estimator of a bounded scale-parameter in a subclass of the exponential family under scale-invariant squared-error loss 总被引:3,自引:0,他引:3
Mohammad Jafari Jozani Nader Nematollahi Khalil Shafie 《Statistics & probability letters》2002,60(4):437-444
A subclass of the scale-parameter exponential family is considered and for the rth power of the scale parameter, which is lower bounded, an admissible minimax estimator under scale-invariant squared-error loss is presented. Also, an admissible minimax estimator of a lower-bounded parameter in the family of transformed chi-square distributions is given. These estimators are the pointwise limits of a sequence of Bayes estimators. Some examples are given. 相似文献
3.
The Aza-Diels-Alder reaction of aldimines with isoeugenol is described. New 1,2,3,4-tetrahydroquinoline and quinoline structures are reported. The stereo- and regioselectivities of the [4+2] cycloaddition are discussed. 相似文献
4.
Khalil Farhadi Ramin Maleki Rouhollah Hosseinzadeh Yamchi Hashem Sharghi Mojtaba Shamsipur 《Analytical sciences》2004,20(5):805-809
[5,10,15,20-Tetrakis(4-N,N-dimethylaminobenzene)porphyrinato]Mn(III) acetate (MnTDPAc) was applied as an ionophore for an iodide-selective PVC membrane electrode. The influences of the membrane composition, pH of the test solution and foreign ions on the electrode performance were investigated. The sensor exhibited not only excellent selectivity to iodide ion compared to Cl- and lipophilic anions such as ClO4- and salicylate, but also a Nernstian response with a slope of -59.4 +/- 1.2 mV per decade for iodide ions over a wide concentration range from 1.0 x 10(-2) to 7.5 x 10(-6) M at 25 degrees C. The potentiometric response was independent of the pH of the solution in the pH range of 2 - 8. The electrode could be used for at least 2 months without any considerable divergence in the potential. Good selectivity for iodide ion, a very short response time, simple preparation and relatively long-term stability were the silent characteristics of this electrode. It was successfully used as an indicator electrode in the potentiometric titration of iodide ions, and also in the determination of iodide from seawater samples and drug formulations. 相似文献
5.
6.
In this paper, we introduce a new concept of semi-preemptive scheduling and we show how it can be used to derive a maximum-flow-based lower bound for the P|rj|Lmax which dominates the well-known preemptive lower bound. We show that, in some cases, the proposed bound strictly dominates the preemptive one while having the same complexity. 相似文献
7.
We consider the rate of convergence for a class of perturbed hemivariational inequalities in reflexive Banach Spaces. Our results can be viewed as an extension and refinement of some previous known results in this area. 相似文献
8.
Mohamed El-Gebeily Donal O'Regan 《Journal of Mathematical Analysis and Applications》2007,334(1):140-156
Existence theory is developed for the equation ?(u)=F(u), where ? is a formally self-adjoint singular second-order differential expression and F is nonlinear. The problem is treated in a Hilbert space and we do not require the operators induced by ? to have completely continuous resolvents. Nonlinear boundary conditions are allowed. Also, F is assumed to be weakly continuous and monotone at one point. Boundary behavior of functions associated with the domains of definitions of the operators associated with ? in the singular case is investigated. A special class of self-adjoint operators associated with ? is obtained. 相似文献
9.
Raed Ali Al-Khasawneh Fudziah Ismail Mohamed Suleiman 《Applied mathematics and computation》2007,190(2):1803-1814
In this paper, third-order 3-stage diagonally implicit Runge–Kutta–Nystrom method embedded in fourth-order 4-stage for solving special second-order initial value problems is constructed. The method has the property of minimized local truncation error as well as the last row of the coefficient matrix is equal to the vector output. The stability of the method is investigated and a standard set of test problems are tested upon and comparisons on the numerical results are made when the same set of test problems are reduced to first-order system and solved using existing Runge–Kutta method. The results clearly shown the advantage and the efficiency of the new method. 相似文献
10.
Effect of Deborah number and phase difference on peristaltic transport of a third-order fluid in an asymmetric channel 总被引:1,自引:0,他引:1
The effect of a third-order fluid on the peristaltic transport in an asymmetric channel is studied. The wavelength of the peristaltic waves is assumed to be large compared to the varying channel width, whereas the wave amplitudes need not be small compared to the varying channel width. The channel asymmetry is produced by choosing the peristaltic wave train on the walls to have different amplitudes and phase. The flow is investigated in a wave frame of reference moving with velocity of the wave. The effects of Deborah number, phase difference, varying channel width and wave amplitudes on the pumping characteristics, streamline pattern and trapping phenomena are investigated. It is observed that the trapping regions increase as the channel becomes more and more symmetric and the trapped bolus volume decreases for increasing Deborah number, phase difference and varying channel width whereas it increases for increasing flow rate and wave amplitudes. Furthermore, the obtained results could also have applications to a range of peristaltic flows for a variety of non-Newtonian fluids such as aqueous solutions of high-molecular weight polyethylene oxide and polyacrylamide. 相似文献