全文获取类型
收费全文 | 7068篇 |
免费 | 207篇 |
国内免费 | 36篇 |
专业分类
化学 | 4228篇 |
晶体学 | 36篇 |
力学 | 412篇 |
数学 | 1477篇 |
物理学 | 1158篇 |
出版年
2023年 | 35篇 |
2022年 | 88篇 |
2021年 | 158篇 |
2020年 | 130篇 |
2019年 | 116篇 |
2018年 | 112篇 |
2017年 | 112篇 |
2016年 | 229篇 |
2015年 | 202篇 |
2014年 | 181篇 |
2013年 | 402篇 |
2012年 | 428篇 |
2011年 | 461篇 |
2010年 | 289篇 |
2009年 | 250篇 |
2008年 | 410篇 |
2007年 | 427篇 |
2006年 | 341篇 |
2005年 | 314篇 |
2004年 | 333篇 |
2003年 | 255篇 |
2002年 | 239篇 |
2001年 | 89篇 |
2000年 | 59篇 |
1999年 | 76篇 |
1998年 | 76篇 |
1997年 | 77篇 |
1996年 | 85篇 |
1995年 | 69篇 |
1994年 | 70篇 |
1993年 | 73篇 |
1992年 | 54篇 |
1991年 | 55篇 |
1990年 | 55篇 |
1989年 | 35篇 |
1988年 | 57篇 |
1987年 | 46篇 |
1986年 | 42篇 |
1985年 | 86篇 |
1984年 | 72篇 |
1983年 | 54篇 |
1982年 | 56篇 |
1981年 | 57篇 |
1980年 | 50篇 |
1979年 | 49篇 |
1978年 | 44篇 |
1977年 | 37篇 |
1976年 | 37篇 |
1975年 | 28篇 |
1974年 | 36篇 |
排序方式: 共有7311条查询结果,搜索用时 16 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.
Vanessa R. Machado Louis P. Sandjo Giovanni L. Pinheiro Milene H. Moraes Mario Steindel Moacir G. Pizzolatti 《Natural product research》2018,32(3):275-281
The natural product lupeol 1 was isolated from aerial parts of Vernonia scorpioides with satisfactory yield, which made it viable to be used as starting material in semisynthetic approach. Ten lupeol derivatives 2–11 were prepared by classical procedures. Including, five new esters derivatives 7–11, which were obtained by structural modifications in the isopropylidene fragment. All semisynthetic compounds and lupeol 1–11 were confirmed by 1H NMR, 13C NMR and HRMS. Their antiprotozoal activity was evaluated in vitro against L. amazonensis and T. cruzi. Derivative 6 showed the best antitrypanosomal activity (IC50 = 12.48 μg/mL) and the lowest cytotoxic derivative (CC50 = 161.50 μg/mL). The mechanism of action of the most active derivatives (4, 6 and 11) is not dependent from the enzyme trypanothione reductase. 相似文献
6.
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
7.
Summary We present an approximation method of a space-homogeneous transport equation which we prove is convergent. The method is very promising for numerical computation. Comparison of a numerical computation with an exact solution is given for the Master equation. 相似文献
8.
9.
Giovanni Carini 《Rendiconti del Circolo Matematico di Palermo》1987,36(1):122-138
In this paper, along with the well established lines of the analytical mechanics, we aim to show an autonomous formulation of the fundamental principle of Lagrange-d'Alembert and of the subsequent Hamilton principle in classical mechanics of deformable continua in the sense that the afore—mentioned principles do not turn out to be a reformulation of the well known undefined equations of motion. 相似文献
10.
Giuseppe Coppola Andrea Irace Giovanni Breglio Mario Iodice Luigi Zeni Antonello Cutolo Pasqualina M. Sarro 《Optics and Lasers in Engineering》2003,39(3):317-332
In this paper we describe two different kind of optoelectronic devices both based on a three terminals active device and exploit the plasma dispersion effect to achieve the desired working. The first device exploits this effect in order to obtain an optical modulation. The second device is an optoelectronic router based on the mode-mixing principle together with the injection-induced optical phase shift. Both devices are integrated into a Silicon on Silicon optical channel waveguide which can be realized using a standard bipolar process. The possibility of using standard, well-known technology presents several advantages with respect to III–V Optoelectronics. The active three terminal device used is a Bipolar Mode Field Effect Transistor (BMFET). Numerical simulation results are presented on both devices. 相似文献