全文获取类型
收费全文 | 1185篇 |
免费 | 15篇 |
国内免费 | 30篇 |
专业分类
化学 | 670篇 |
晶体学 | 6篇 |
力学 | 33篇 |
数学 | 373篇 |
物理学 | 148篇 |
出版年
2018年 | 7篇 |
2016年 | 18篇 |
2015年 | 9篇 |
2014年 | 17篇 |
2013年 | 75篇 |
2012年 | 32篇 |
2011年 | 39篇 |
2010年 | 29篇 |
2009年 | 33篇 |
2008年 | 41篇 |
2007年 | 38篇 |
2006年 | 42篇 |
2005年 | 35篇 |
2004年 | 47篇 |
2003年 | 45篇 |
2002年 | 43篇 |
2001年 | 24篇 |
2000年 | 27篇 |
1999年 | 10篇 |
1998年 | 12篇 |
1997年 | 22篇 |
1996年 | 25篇 |
1995年 | 25篇 |
1994年 | 7篇 |
1993年 | 23篇 |
1992年 | 10篇 |
1991年 | 18篇 |
1990年 | 14篇 |
1989年 | 14篇 |
1988年 | 18篇 |
1987年 | 21篇 |
1986年 | 11篇 |
1985年 | 26篇 |
1984年 | 20篇 |
1983年 | 18篇 |
1982年 | 27篇 |
1981年 | 27篇 |
1980年 | 29篇 |
1979年 | 28篇 |
1978年 | 19篇 |
1977年 | 19篇 |
1976年 | 20篇 |
1975年 | 13篇 |
1974年 | 14篇 |
1973年 | 16篇 |
1972年 | 11篇 |
1971年 | 8篇 |
1970年 | 7篇 |
1967年 | 7篇 |
1966年 | 7篇 |
排序方式: 共有1230条查询结果,搜索用时 15 毫秒
51.
Mehdi Moini Donald Chace Fred P. Abramson 《Journal of the American Society for Mass Spectrometry》1991,2(3):250-255
Addition of a reactant gas to a low pressure microwave-induced plasma creates a reaction interface in which complex molecules are converted into small polyatomic neutral species. For a given reactant gas the array of these small molecules reflect s the elemental composition of the original analyte. In this study HCI has been found highly effective as a reactant gas for selective detection of sulfur-eontaining compounds using capillary gas chromatography/ chernical reaction interface mass spectrometry. Detection limits as low as 30 pg of a sulfur-containing compound and a dynamic range of two orders of magnitude were achieved. 相似文献
52.
Peter Sörös Jonathan Marmurek Fred Tam Nicole Baker W Richard Staines Simon J Graham 《BMC neuroscience》2007,8(1):48
Background
Focal lesions of the frontal, parietal and temporal lobe may interfere with tactile working memory and attention. To characterise the neural correlates of intact vibrotactile working memory and attention, functional MRI was conducted in 12 healthy young adults. Participants performed a forced-choice vibrotactile frequency discrimination task, comparing a cue stimulus of fixed frequency to their right thumb with a probe stimulus of identical or higher frequency. To investigate working memory, the time interval between the 2 stimuli was pseudo-randomized (either 2 or 8 s). To investigate selective attention, a distractor stimulus was occasionally presented contralaterally, simultaneous to the probe. 相似文献53.
莫晓虎 张建勇 张清江 Achasov Mikhail 蔡啸 傅成栋 Harris Fred 刘倩 Muchnoi Nikolay 秦庆 屈化民 王贻芳 徐金强 张天保 《中国物理 C》2011,35(7):642-655
Understanding the radiation background at the north crossing point (NCP) in the tunnel of BEPCII is crucial for the performance safety of the High Purity Germanium (HPGe) detector, and in turn of great significance for long-term stable running of the energy measurement system. Therefore, as the first step, a NaI(Tl) detector is constructed to continuously measure the radiation level of photons as background for future experiments. Furthermore, gamma and neutron dosimeters are utilized to explore the radiation distribution in the vicinity of the NCP where the HPGe detector will be located. Synthesizing all obtained information, the shielding for neutron irradiation is studied based on model-dependent theoretical analysis. 相似文献
54.
James B Whitney Saied Mirshahidi So-Yon Lim Lauren Goins Chris C Ibegbu Daniel C Anderson Richard B Raybourne Fred R Frankel Judy Lieberman Ruth M Ruprecht 《Journal of immune based therapies and vaccines》2011,9(1):2
Background
We have evaluated an attenuated Listeria monocytogenes (Lm) candidate vaccine vector in nonhuman primates using a delivery regimen relying solely on oral vaccination. We sought to determine the impact of prior Lm vector exposure on the development of new immune responses against HIV antigens. 相似文献55.
We study the positivity preserving properties of the heat equation with a white noise potential and random initial condition. Moreover, we find a generalized Feynman--Kac formula for the solution of the problem using methods from the white noise analysis. The initial condition can anticipate the driving white noise. We show that the solution is positive, when the random initial condition is positive. For the case of a time-dependent white noise potential, we give a special representation of the solution together with regularity results. 相似文献
56.
If is a family of sets, its intersection graph has the sets in as vertices and an edge between two sets if and only if they overlap. This paper investigates the concept of boxicity of a graph G, the smallest n such that G is the intersection graph of boxes in Euclidean n-space. The boxicity, b(G), was introduced by Roberts in 1969 and has since been studied by Cohen, Gabai, and Trotter. The concept has applications to niche overlap (competition) in ecology and to problems of fleet maintenance in operations research. These applications will be described briefly. While the problem of computing boxicity is in general a difficult problem (it is NP-complete), this paper develops techniques for computing boxicity which give useful bounds. They are based on the simple observation that b(G)≤k if and only if there is an edge covering of by spanning subgraphs of , each of which is a cointerval graph, the complement of an interval graph (a graph of boxicity ≤1.). 相似文献
57.
Fred B. Weissler 《Israel Journal of Mathematics》1978,29(2-3):265-275
Under certain circumstances, the Trotter-Lie formulaW
t=lim(U
t/nVt/n)
n
is used to construct a non-linear semi-groupW
t on closed subsets ofL
P, 1≦p<∞. In particular we consider the situation whereU
t=e
tA is a positivity preservingC
0 (linear) semi-group andV
t is generated by a (non-linear) functionF with certain monotonicity properties. In general,A andF are “singular” onL
p and no requirement is made that one of them be “relatively bounded” with respect to the other. The generator of the resulting
semi-groupW
t turns out to be an extension ofA +F restricted to a suitable domain.
Research supported by a Danforth Graduate Fellowship and a Weizmann Postdoctoral Fellowship. 相似文献
58.
To investigate the structure of number sense and then to assess its uses in fifth‐grade children's number sense development, a computerized number sense scale was developed and evaluated. The findings of the study indicate that the newly developed scale, with four dominant factors identified and reconfirmed, is internally consistent and substantially valid. It can be reliably used as a screening measure for a quick check of students' number sense development via online self‐assessment. Compared with our previous study, both qualitative and quantitative changes were detected in students' number sense development at different grades. The qualitative change in number sense development is manifested in different numbers of factor components produced at different grades. The quantitative change is manifested in different amounts of factor variance explained at different grades. Furthermore, among the four aspects of number sense, Taiwanese students perform best on recognizing the relative number size yet relatively worse on judging the reasonableness of computational results. 相似文献
59.
Carl Bender Fred Cooper L. M. Simmons Jr. Pinaki Roy Greg Kilcup 《Journal of statistical physics》1991,64(1-2):395-428
We discuss the randomly driven systemdx/dt= -W(x) +f(t), wheref(t) is a Gaussian random function or stirring force withf(t)f(t)=2(t–t), andW(x) is of the formgx
1+2. The parameter is a measure of the nonlinearity of the equation. We show how to obtain the correlation functionsx(t)f(t)···x(t(
n))
f
as a power series in. We obtain three terms in the expansion and show how to use Padé approximants to analytically continue the answer in the variable. By using scaling relations, we show how to get a uniform approximation to the equal-time correlation functions valid for allg and. 相似文献
60.