全文获取类型
收费全文 | 1845篇 |
免费 | 49篇 |
国内免费 | 14篇 |
专业分类
化学 | 1368篇 |
晶体学 | 21篇 |
力学 | 19篇 |
数学 | 59篇 |
物理学 | 441篇 |
出版年
2023年 | 8篇 |
2021年 | 18篇 |
2020年 | 13篇 |
2019年 | 26篇 |
2018年 | 13篇 |
2017年 | 13篇 |
2016年 | 31篇 |
2015年 | 27篇 |
2014年 | 42篇 |
2013年 | 78篇 |
2012年 | 83篇 |
2011年 | 88篇 |
2010年 | 40篇 |
2009年 | 48篇 |
2008年 | 97篇 |
2007年 | 107篇 |
2006年 | 104篇 |
2005年 | 107篇 |
2004年 | 113篇 |
2003年 | 101篇 |
2002年 | 77篇 |
2001年 | 60篇 |
2000年 | 57篇 |
1999年 | 32篇 |
1998年 | 18篇 |
1997年 | 15篇 |
1996年 | 16篇 |
1995年 | 19篇 |
1994年 | 23篇 |
1993年 | 24篇 |
1992年 | 36篇 |
1991年 | 21篇 |
1990年 | 21篇 |
1989年 | 20篇 |
1988年 | 23篇 |
1987年 | 24篇 |
1986年 | 17篇 |
1985年 | 33篇 |
1984年 | 21篇 |
1983年 | 13篇 |
1982年 | 10篇 |
1981年 | 10篇 |
1980年 | 11篇 |
1979年 | 20篇 |
1978年 | 22篇 |
1977年 | 13篇 |
1976年 | 12篇 |
1974年 | 17篇 |
1973年 | 22篇 |
1967年 | 7篇 |
排序方式: 共有1908条查询结果,搜索用时 15 毫秒
1.
Given an ‐vertex pseudorandom graph and an ‐vertex graph with maximum degree at most two, we wish to find a copy of in , that is, an embedding so that for all . Particular instances of this problem include finding a triangle‐factor and finding a Hamilton cycle in . Here, we provide a deterministic polynomial time algorithm that finds a given in any suitably pseudorandom graph . The pseudorandom graphs we consider are ‐bijumbled graphs of minimum degree which is a constant proportion of the average degree, that is, . A ‐bijumbled graph is characterised through the discrepancy property: for any two sets of vertices and . Our condition on bijumbledness is within a log factor from being tight and provides a positive answer to a recent question of Nenadov. We combine novel variants of the absorption‐reservoir method, a powerful tool from extremal graph theory and random graphs. Our approach builds on our previous work, incorporating the work of Nenadov, together with additional ideas and simplifications. 相似文献
2.
Jumiarti Agus Hideki Abe Yoshiharu Doi Takeharu Tsuge 《Polymer Degradation and Stability》2006,91(8):1645-1650
Polyhydroxyalkanoate (PHA) synthase (PhaC) from Wautersia eutropha was expressed in a wide range of production level in Escherichia coli XL1-Blue cells and its effects on PhaC activity, poly[(R)-3-hydroxybutyrate] [P(3HB)] production and its molecular weights were investigated. The production level of PhaC was controlled both by the amount of chemical inducer (isopropyl-β-d-thiogalactopyranoside, IPTG) added into the medium and the use of different copy number of plasmids. In a flask experiment, as PhaC production level in the cells increased, the PhaC activity also increased in the range of low PhaC concentration. However, PhaC activity did not further increase in the range of high PhaC concentration, probably due to the formation of inclusion body in the cells. The molecular weight of P(3HB) was found to decrease with increasing PhaC activity. This trend was also verified in high cell density cultivation using 10-l jar fermentor. Furthermore, we demonstrated that the use of low copy number plasmid and appropriate induction of PhaC expression were effective in achieving both high productivity and high molecular weight of P(3HB). 相似文献
3.
T. Ishii M. Asai A. Makishima I. Hossain P. Kleinheinz M. Ogawa M. Matsuda S. Ichikawa 《The European Physical Journal A - Hadrons and Nuclei》2002,13(1-2):15-19
Nuclei in the neutron-rich Ni region have been studied by γ-ray spectroscopy. Gamma-rays emitted from isomers, with T
1/2 > 1 ns, produced in heavy-ion deep-inelastic collisions were measured with an isomer-scope. The nuclear structure of the
doubly magic 68Ni and its neighbor 69,71Cu is discussed on the basis of the shell model. Future experiments for more neutron-rich Ni nuclei are also viewed.
Received: 1 May 2001 / Accepted: 4 December 2001 相似文献
4.
Mark Doyle Susan A. Mulligan Tetsuya Matsuda Gerald M. Pohost 《Magnetic resonance imaging》1992,10(6):887-892
A new “bright blood” strategy, outflow refreshment imaging, is introduced in which a number of overlapping slices are excited in rapid succession. Flowing spins that refresh each overlapped slice portion contribute a bright signal. Additionally, static tissue in each non-overlapped slice portion also yields a bright signal. However, the flow/static contrast is comparable to that produced in inflow refreshment images, and angiograms can be generated by conventional maximum intensity projection processing. The dual ability to visualize angiograms and static tissue images is a major benefit of the strategy. Computer simulations of flow sensitivities and in vivo results are presented which compare the outflow and inflow refreshment imaging strategies. 相似文献
5.
在粗糙表面上用液晶空间光调制器进行振动测量 总被引:2,自引:2,他引:0
为实现在一段时间内连续实时观测振动物体的全息干涉图形,采用覆盖铝箔的喇叭作为振动物体,利用铝箔原有未经特殊处理表面反射的漫反射光成像,并用光寻址液晶空间光调制器(Liquid crystal-sparial lightmodulator,LC-SLM)作为全息记录载体,来实现振动测量。实验中采用时间平均干涉测量法,得到了不同振动频率下物体的干涉图形。同时在连续改变振动物体的振动频率时,可以清晰地观察到物体振动全息干涉图形的变化过程,即近实时的全息干涉图形。 相似文献
6.
We synthesized TPP[FeIII(Pc)(CN)2]2, PTMAx[FeIII(Pc)(CN)2]·y(MeCN), and PXX [FeIII(Pc)(CN)2], a new series of charge-transfer salts containing the axially-substituted phthalocyanine (Pc), [FeIII(Pc)(CN)2]−. In this molecular unit, the π conduction electron derived from the Pc-ring coexists with the d electron which is a potential source of a local magnetic moment. Therefore various phenomena associated with the interplay between local magnetic moments and conduction electrons are expected. We observed the giant negative magnetoresistance (GNMR) in all the three salts. The GNMR is highly anisotropic for the magnetic-field direction, and reflects the g-tensor anisotropy of the local magnetic moment in the [FeIII(Pc)(CN)2]− unit. This indicates that the GNMR in these salts originates from the strong π-d interaction in the [FeIII(Pc)(CN)2]− unit. 相似文献
7.
8.
Dong Hwan Choi Yoshio Katakura Rieko Matsuda Yuzuru Hayashi Masato Hirobe Yasuhiro Goda Kazuaki Ninomiya Suteaki Shioya 《Analytical sciences》2007,23(2):215-218
The mathematical model for predicting the precision, limit of detection (LOD) and range of quantitation (ROQ) in a competitive enzyme-linked immunosorbent assay (ELISA) proposed by Hayashi et al. (Anal. Chem., 2004, 76, 1295) was validated. The model describes the relative standard deviation (RSD) of concentration estimates by the RSDs of pipetting volumes of analyte, enzyme-conjugated antigen, antibody and substrate solutions, and the standard deviation (SD) of inherent absorbances between the wells in an ELISA plate. For 6 kinds of direct competitive ELISA kits, the LOD and ROQ predicted by the model agreed well with those obtained by experiments with real samples. It was also confirmed that the model is applicable to the prediction of uncertainty that depends on the pipetting error of the viscous antiserum solution. The model was demonstrated to be useful for estimating the LOD and ROQ of competitive ELISA. 相似文献
9.
10.
B. F. Araujo H. T. Matsuda T. A. Kuada J. A. Araujo 《Journal of Radioanalytical and Nuclear Chemistry》1992,166(1):75-83
In the actinide separation process using TBP as extractant, hydrolytic and radiolytic reactions cause a gradual decomposition of the extractant, resulting in the formation of degradation products which can affect process performance adversely. The TBP diluent has to be cleaned from these degradation products before it is reused. This paper deals with a procedure for solvent cleanup, using a fourstage continuous contactor for increasing the scrubbing efficiency. 相似文献