全文获取类型
收费全文 | 2358篇 |
免费 | 81篇 |
国内免费 | 9篇 |
专业分类
化学 | 1963篇 |
晶体学 | 12篇 |
力学 | 25篇 |
数学 | 221篇 |
物理学 | 227篇 |
出版年
2023年 | 24篇 |
2022年 | 45篇 |
2021年 | 68篇 |
2020年 | 48篇 |
2019年 | 59篇 |
2018年 | 40篇 |
2017年 | 37篇 |
2016年 | 81篇 |
2015年 | 85篇 |
2014年 | 82篇 |
2013年 | 116篇 |
2012年 | 150篇 |
2011年 | 201篇 |
2010年 | 119篇 |
2009年 | 109篇 |
2008年 | 152篇 |
2007年 | 153篇 |
2006年 | 114篇 |
2005年 | 121篇 |
2004年 | 100篇 |
2003年 | 93篇 |
2002年 | 74篇 |
2001年 | 37篇 |
2000年 | 20篇 |
1999年 | 34篇 |
1998年 | 17篇 |
1997年 | 13篇 |
1996年 | 23篇 |
1995年 | 23篇 |
1994年 | 21篇 |
1993年 | 15篇 |
1992年 | 11篇 |
1991年 | 13篇 |
1990年 | 20篇 |
1989年 | 16篇 |
1988年 | 10篇 |
1987年 | 6篇 |
1986年 | 5篇 |
1985年 | 15篇 |
1984年 | 9篇 |
1983年 | 5篇 |
1982年 | 12篇 |
1980年 | 8篇 |
1979年 | 12篇 |
1978年 | 9篇 |
1976年 | 4篇 |
1975年 | 4篇 |
1974年 | 3篇 |
1970年 | 2篇 |
1967年 | 2篇 |
排序方式: 共有2448条查询结果,搜索用时 15 毫秒
121.
Summary A method is described for roughening the surface of sodalime glass capillaries by depositing sodium chloride dendrites on
the inner wall. The sodium chloride layer improves the wettability of the wall and shows favourable adsorption properties.
For apolar and polar stationary phases coating efficiencies of 60 to 85% are attained. 相似文献
122.
Sandra Spiroff 《Journal of Pure and Applied Algebra》2004,186(1):77-89
Let A be an excellent local normal domain and {fn}n=1∞ a sequence of elements lying in successively higher powers of the maximal ideal, such that each hypersurface A/fnA satisfies R1. We investigate the injectivity of the maps Cl(A)→Cl((A/fnA)′), where (A/fnA)′ represents the integral closure. The first result shows that no non-trivial divisor class can lie in every kernel. Secondly, when A is, in addition, an isolated singularity containing a field of characteristic zero, dim A?4, and A has a small Cohen-Macaulay module, then we show that there is an integer N>0 such that if , then Cl(A)→Cl((A/fnA)′) is injective. We substantiate these results with a general construction that provides a large collection of examples. 相似文献
123.
124.
Solid phase microextraction in combination with capillary GC-MS was used as monitoring technique for the collection and detection of the fungal volatile metabolite (+)-aristolochene by sporulated surface cultures of Penicillium roqueforti. A comparison was made between different toxigenic and nontoxigenic strains of P. roqueforti. Different growth conditions and media, such as malt extract agar, potato dextrose agar and sabouraud dextrose agar were compared. Whereas toxigenic strains produced large amounts of (+)-aristolochene, beta-elemene, valencene and germacrene A, nontoxigenic P. roqueforti strains showed a remarkably different headspace profile, in which ethyl-2-hexenoate, E-beta-caryophyllene, aromadendrene and beta-patchoulene were the predominant volatiles, apart from other sesquiterpene hydrocarbons present at lower concentrations. Stir bar sorptive extraction, was also applied in the headspace sampling mode, i.e. headspace sorptive extraction (HSSE) for the enrichment of fungal volatiles from sporulated surface cultures to differentiate between toxigenic and nontoxigenic fungi. Hence, it can be concluded that headspace analysis of volatile fungal metabolites by SPME and HSSE in combination with capillary GC-MS is a suitable monitoring technique for the fast detection of mycotoxin producing fungi. 相似文献
125.
Loss S Magistrato A Cataldo L Hoffmann S Geoffroy M Röthlisberger U Grützmacher H 《Angewandte Chemie (International ed. in English)》2001,40(7):1143
The cover picture shows the metalloporphyrin heterodimer [(tpp)Mo$\rm{\mathop{-}^{4}}$Re(oep)](+) with the novel [Mo$\rm{\mathop{-}^{4}}$Re](5+) core. The core represents the first example of a quadruple bond between elements of different triads, thus proving that heterometallic quadruple bonds are not limited to the Group 6 metals. From the space-filling model it is clear that there is no interaction between the stabilizing porphyrin ligands. The ORTEP plot in a projection along the Re-Mo axis emphasizes the perfectly eclipsed geometry of the porphyrins, which is unambiguous proof of the existence of the quadruple bond in the solid state. The diamagnetism and large magnetic anisotropy of the cation, as determined by (1)H NMR spectroscopy, indicate that the quadruple bond is retained in solution. A logical and well-defined synthetic route was used to synthesize the dimer, and can be extended to other metalloporphyrins to generate further novel quadruple bonds (the picture was generated by Marina Boulan, St. Petersburg, Russia), full details are reported by J. P. Collman et al. on p. 1271 ff. 相似文献
126.
Regina Sandra Burachik B. F. Svaiter 《Proceedings of the American Mathematical Society》2003,131(8):2379-2383
Recently, the authors studied the connection between each maximal monotone operator and a family of convex functions. Each member of this family characterizes the operator and satisfies two particular inequalities.
The aim of this paper is to establish the converse of the latter fact. Namely, that every convex function satisfying those two particular inequalities is associated to a unique maximal monotone operator.
127.
The aim of this paper is to study necessary conditions for existence of weak solutions of the inequality
128.
D. Keith Wilson Vladimir E. Ostashev Sandra L. Collier David F. Aldridge 《Applied Acoustics》2007,68(2):173-200
A time-domain formulation for sound propagation in rigid-frame porous media, including waveform attenuation and dispersion, is developed. The new formulation is based on inversion of the relaxation functions from a previous model [Wilson DK, Ostashev VE, Collier SL. J Acoust Soc Am 2004;116:1889-92], thereby casting the convolution integrals in a form amenable to numerical implementation. Numerical techniques are developed that accurately implement the relaxational equations and transparently reduce to previous results in low- and high-frequency limits. The techniques are demonstrated on calculations of outdoor sound propagation involving hills, barriers, and ground surfaces with various material properties. We also compare the relaxation formulation to a widely applied phenomenological model developed by Zwikker and Kosten. The two models can be made equivalent if the resistance constant, structure constant, and compression modulus in the ZK model are allowed to be weakly frequency dependent. But if the ZK parameters are taken to be constant, as is typically the case, the relaxation model provides more accurate calculations of attenuation by acoustically soft porous materials such as snow, gravel, and forest litter. 相似文献
129.
Jorge Bravo Sandra Bolaño Luca Gonsalvi Maurizio Peruzzini 《Coordination chemistry reviews》2010,254(5-6):555-607
This review paper covers the recent developments (2004–2009) on the tailored synthetic modifications and related coordination chemistry of the water-soluble cage-like aminophosphine ligand 1,3,5-triaza-7-phosphatricyclo-[3.3.1.1]decane (PTA), together with the new applications in the fields of catalysis, material science and medicinal chemistry. 相似文献
130.