全文获取类型
收费全文 | 39416篇 |
免费 | 1486篇 |
国内免费 | 54篇 |
专业分类
化学 | 26810篇 |
晶体学 | 351篇 |
力学 | 746篇 |
数学 | 5737篇 |
物理学 | 7312篇 |
出版年
2023年 | 293篇 |
2022年 | 262篇 |
2021年 | 494篇 |
2020年 | 642篇 |
2019年 | 604篇 |
2018年 | 822篇 |
2017年 | 765篇 |
2016年 | 1435篇 |
2015年 | 1190篇 |
2014年 | 1212篇 |
2013年 | 2495篇 |
2012年 | 2736篇 |
2011年 | 2922篇 |
2010年 | 1762篇 |
2009年 | 1448篇 |
2008年 | 2462篇 |
2007年 | 2416篇 |
2006年 | 2136篇 |
2005年 | 1938篇 |
2004年 | 1602篇 |
2003年 | 1207篇 |
2002年 | 1101篇 |
2001年 | 794篇 |
2000年 | 714篇 |
1999年 | 524篇 |
1998年 | 408篇 |
1997年 | 315篇 |
1996年 | 441篇 |
1995年 | 297篇 |
1994年 | 304篇 |
1993年 | 332篇 |
1992年 | 317篇 |
1991年 | 254篇 |
1990年 | 224篇 |
1989年 | 208篇 |
1988年 | 192篇 |
1987年 | 184篇 |
1986年 | 180篇 |
1985年 | 244篇 |
1984年 | 214篇 |
1983年 | 168篇 |
1982年 | 159篇 |
1981年 | 162篇 |
1980年 | 124篇 |
1979年 | 149篇 |
1978年 | 131篇 |
1977年 | 123篇 |
1976年 | 134篇 |
1975年 | 109篇 |
1973年 | 123篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
191.
Katalin E. Kövér Dušan Uhr?&#x;n Victor J. Hruby 《Journal of magnetic resonance (San Diego, Calif. : 1997)》1998,130(2):162-168
A pulsed field gradient version of the sensitivity-enhanced 2D TOCSY experiment is proposed which yields high-quality spectra with improved sensitivity and a minimum of two scans pert1increment. For rapid acquisition of 1D TOCSY spectra, the 1D DPFGSE–TOCSY experiment was modified to include phase-encoded multiple-selective excitation followed by a simple spectral editing. Combination of these two building blocks is used in a sensitivity-enhanced 2D analog of the 3D TOCSY–TOCSY experiment which provides an efficient tool for resolving severely overlapped signals of oligomers in short experimental time. 相似文献
192.
Wojciech Bocian Jarosław Jaźwínski Lech Stefaniak Graham A. Webb 《Chemistry of Heterocyclic Compounds》1995,31(9):1103-1107
1H,13C,14N and15N NMR measurements are reported for four mesoionic 1-oxa-2, 3, 4-triazoles containing exocyclic nitrogenous groups. The NMR signal assignments are discussed and compared with those previously published for some corresponding oxatriazoles. The results obtained support the proposed cyclic mesoionic structures for the compounds studied. The questions of possible charge delocalization and valence tautomerism are addressed. Compound with N– H as a exocyclic group (Fig. 1) is found to be relatively unstable, this is attributed to proton migration in the corresponding non-cyclic form of this molecule.Published in Khimiya Geterotsikiicheskikh Soedinenii, No. 9, pp. 1260–1263, September, 1995. 相似文献
193.
In this paper we describe the general forms of all (nonlinear) continuous functionals on the sets of positive definite, positive semi-definite and Hermitian matrices which are multiplicative on the commuting elements. As a consequence, we obtain some new characterizations of the determinant on those classes of matrices.
194.
This article explores the use of geometric algebra in linear and multilinear algebra, and in affine, projective and conformal geometries. Our principal objective is to show how the rich algebraic tools of geometric algebra are fully compatible with and augment the more traditional tools of matrix algebra. The novel concept of an h-twistor makes possible a simple new proof of the striking relationship between conformal transformations in a pseudo-Euclidean space to isometries in a pseudo-Euclidean space of two higher dimensions. The utility of the h-twistor concept, which is a generalization of the idea of a Penrose twistor to a pseudo-Euclidean space of arbitrary signature, is amply demonstrated in a new treatment of the Schwarzian derivative. 相似文献
195.
Lubomír Kubáček 《Mathematica Slovaca》2007,57(1):59-82
In some situations estimates of unknown parameters must be corrected by additional measurements. It is in principle no problem
to calculate the corrected estimates, however, it is of more interest to find formulae for correction itself. The formulae
enable us to design an additional experiment and to judge its usefulness.
The aim of the paper is to find such formulae for several situations.
Supported by the grant of the Council of Czech Government MSM 6 198 959 214. 相似文献
196.
We present a construction which shows that some special continua do not have the nonwandering-eventually-periodic property. The construction applies e.g. to the topologist's sin curve and to the harmonic fan. 相似文献
197.
We investigate traces of functions, belonging to a class of functions with dominating mixed smoothness in ℝ3, with respect to planes in oblique position. In comparison with the classical theory for isotropic spaces a few new phenomenona
occur. We shall present two different approaches. One is based on the use of the Fourier transform and restricted to p = 2. The other one is applicable in the general case of Besov-Lizorkin-Triebel spaces and based on atomic decompositions. 相似文献
198.
Anette Munch Elmr Patric Jannasch 《Journal of polymer science. Part A, Polymer chemistry》2006,44(7):2195-2205
Methacrylate‐functionalized poly(ethylene oxide‐co‐ethylene carbonate) macromonomers were prepared in two steps by the anionic ring‐opening polymerization of ethylene carbonate at 180 °C, with potassium methoxide as the initiator, followed by the reaction of the terminal hydroxyl groups of the polymers with methacryloyl chloride. The molecular weight of the polymer went through a maximum after approximately 45 min of polymerization, and the content of ethylene carbonate units in the polymer decreased with the reaction time. A polymer having a number‐average molecular weight of 2650 g mol?1 and an ethylene carbonate content of 28 mol % was selected and used to prepare a macromonomer, which was subsequently polymerized by UV irradiation in the presence of different concentrations of lithium bis(trifluoromethanesulfonyl)imide salt. The resulting self‐supportive crosslinked polymer electrolyte membranes reached ionic conductivities of 6.3 × 10?6 S cm?1 at 20 °C. The coordination of the lithium ions by both the ether and carbonate oxygens in the polymer structure was indicated by Fourier transform infrared spectroscopy. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2195–2205, 2006 相似文献
199.
akir Aydoan Mustafa Salam Abdulmecit Türüt 《Journal of Polymer Science.Polymer Physics》2006,44(11):1572-1579
The polypyrrole/p‐InP structure has been fabricated by the electrochemical polymerization of the organic polypyrrole onto the p‐InP substrate. The current–voltage (I–V), capacitance–voltage (C–V), and capacitance–frequency (C–f) characteristics of the PPy/p‐InP structure have been determined at room temperature. The structure showed nonideal I–V behavior with the ideality factor and the barrier height 1.48 and 0.69 eV respectively. C–f measurements of the structure have been carried out using the Schottky capacitance spectroscopy technique and it has been seen that there is a good agreement between the experimental and theoretical values. Also, it has been seen that capacitance almost show a plateau up to a certain value of frequency, after which, the capacitance decreases. The higher values of capacitance at low frequencies were attributed to the excess capacitance resulting from the interface states in equilibrium with the p‐InP that can follow the a.c. signal. The interface state density Nss and relaxation time τ of the structure were determined from C–f characteristics. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 1572–1579, 2006 相似文献
200.