全文获取类型
收费全文 | 31983篇 |
免费 | 184篇 |
国内免费 | 291篇 |
专业分类
化学 | 12244篇 |
晶体学 | 281篇 |
力学 | 1600篇 |
综合类 | 12篇 |
数学 | 9630篇 |
物理学 | 8691篇 |
出版年
2022年 | 59篇 |
2021年 | 79篇 |
2020年 | 73篇 |
2019年 | 75篇 |
2018年 | 1225篇 |
2017年 | 1492篇 |
2016年 | 811篇 |
2015年 | 639篇 |
2014年 | 556篇 |
2013年 | 838篇 |
2012年 | 3310篇 |
2011年 | 2479篇 |
2010年 | 1921篇 |
2009年 | 1644篇 |
2008年 | 733篇 |
2007年 | 789篇 |
2006年 | 747篇 |
2005年 | 4564篇 |
2004年 | 4067篇 |
2003年 | 2417篇 |
2002年 | 608篇 |
2001年 | 326篇 |
2000年 | 119篇 |
1999年 | 207篇 |
1998年 | 149篇 |
1997年 | 112篇 |
1996年 | 95篇 |
1995年 | 83篇 |
1994年 | 85篇 |
1993年 | 51篇 |
1992年 | 204篇 |
1991年 | 180篇 |
1990年 | 162篇 |
1989年 | 124篇 |
1988年 | 131篇 |
1987年 | 83篇 |
1986年 | 62篇 |
1985年 | 80篇 |
1984年 | 62篇 |
1983年 | 57篇 |
1982年 | 51篇 |
1981年 | 49篇 |
1979年 | 58篇 |
1978年 | 43篇 |
1976年 | 94篇 |
1975年 | 52篇 |
1974年 | 57篇 |
1973年 | 53篇 |
1972年 | 40篇 |
1968年 | 39篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
1.
Meccanica - The static limit analysis of axially symmetric masonry domes subject to pseudo-static seismic forces is addressed. The stress state in the dome is represented by the shell stress... 相似文献
2.
Carello Giuliana Landa Paolo Tnfani Elena Testi Angela 《Central European Journal of Operations Research》2022,30(1):159-187
Central European Journal of Operations Research - In the past years, the number of patients in need of chemotherapy treatments has been constantly increasing. Chemotherapy treatments must be... 相似文献
3.
Vito Gigante Laura Aliotta Maria Beatrice Coltelli Patrizia Cinelli Luigi Botta Francesco Paolo La Mantia Andrea Lazzeri 《Journal of polymer science. Part A, Polymer chemistry》2020,58(23):3264-3282
The development of biodegradable materials for tailored applications, particularly in the field of polymeric films and sheets, is a challenging technological goal as well as a contribution to help protect the environment. Poly(lactic) acid (PLA) is a promising substitute for several oil-based polymers; however, to overcome its thermal and mechanical drawbacks, researchers have developed solutions such as blending PLA with polybutylene adipate terephthalate (PBAT), which is capable of increasing the ductility of the final material. In this study, PLA/PBAT binary blends, with minimum possible content of nonrenewable materials, were examined from processing, thermal, morphological, and rheological perspective. An optimized PLA/PBAT ratio was chosen as the polymeric basis to obtain a biodegradable formulation by adding a biobased plasticizer and appropriate fillers to produce a micrometer film with tailored flexibility and tear resistance. The processing technology involved flat-die extrusion, followed by calendering. The tearing resistance of the produced film was investigated, and the results were compared with literature data. A study on the essential work of fracture was implemented to explore the mode III out-of-plane fracture resistance starting from a trouser tear test. 相似文献
4.
5.
Paolo Bertozzini Roberto Conti Roberto Longo 《Communications in Mathematical Physics》1998,193(2):471-492
Let ? be a local conformal net of von Neumann algebras on S
1 and ρ a M?bius covariant representation of ?, possibly with infinite dimension. If ρ has finite index, ρ has automatically
positive energy. If ρ has infinite index, we show the spectrum of the energy always to contain the positive real line, but,
as seen by an example, it may contain negative values. We then consider nets with Haag duality on ℝ, or equivalently sectors
with non-solitonic extension to the dual net; we give a criterion for irreducible sectors to have positive energy, namely
this is the case iff there exists an unbounded M?bius covariant left inverse. As a consequence the class of sectors with positive
energy is stable under composition, conjugation and direct integral decomposition.
Received: 21 April 1997 / Accepted: 23 September 1997 相似文献
6.
Julia K Pruns Jens-Peter Vietzke Manfred Strassner Claudius Rapp Ulrich Hintze Wilfried A K?nig 《Rapid communications in mass spectrometry : RCM》2002,16(3):208-211
A new solvent-free sample preparation method using silver trifluoroacetate (AgTFA) was developed for the analysis of low molecular weight paraffins and microcrystalline waxes by laser desorption/ionization time-of-flight mass spectrometry (LDI-TOFMS). Experiments show that spectral quality can be enhanced by dispersing AgTFA directly in liquid paraffins without the use of additional solvents. This preparation mixture is applied directly to the MALDI probe. Solid waxes could be examined by melting prior to analysis. The method also provides sufficiently reproducible spectra that peak area ratios between mono- and bicyclic alkane peaks indicated variations in the cycloalkane content of paraffin samples. Dehydrogenation of hydrocarbons observed during the desorption/ionization process was studied by analysis of alkane standards. 相似文献
7.
The versatile behavior of a trihydrazidophosphoradamantane allowing the synthesis of a variety of neutral, mono- or di-cationic water-soluble molecules of potential interest for biphasic catalysis is reported. 相似文献
8.
In this paper we construct an example of a word metric on an infinite cyclic subgroup. This example shows that subexponential
distortion does not obstruct non-trivial growth of connected radii. This answers a question of Gromov [6]. The constructed
metric has other pathological properies. Specifically, its asymptotic cone depends on the choice of ultrafilter and scaling
sequence.
The work has been partially supported by the Swiss National Science Foundation. 相似文献
9.
We build a metric space which is homeomorphic to a Cantor set but cannot be realized as the attractor of an iterated function system. We give also an example of a Cantor set K in R3 such that every homeomorphism f of R3 which preserves K coincides with the identity on K. 相似文献
10.
Milan Medved? 《Journal of Mathematical Analysis and Applications》2002,267(2):643-650
A criterion for the nonexplosion of solutions to semilinear evolution equations on Banach spaces is proved. The result is obtained by applying a modification of the Bihari type inequality to the case of a weakly singular nonlinear integral inequality. 相似文献