全文获取类型
收费全文 | 5655篇 |
免费 | 825篇 |
国内免费 | 399篇 |
专业分类
化学 | 1265篇 |
晶体学 | 41篇 |
力学 | 1281篇 |
综合类 | 60篇 |
数学 | 761篇 |
物理学 | 1629篇 |
无线电 | 1842篇 |
出版年
2024年 | 20篇 |
2023年 | 82篇 |
2022年 | 203篇 |
2021年 | 216篇 |
2020年 | 247篇 |
2019年 | 188篇 |
2018年 | 189篇 |
2017年 | 227篇 |
2016年 | 269篇 |
2015年 | 231篇 |
2014年 | 355篇 |
2013年 | 405篇 |
2012年 | 337篇 |
2011年 | 381篇 |
2010年 | 316篇 |
2009年 | 318篇 |
2008年 | 292篇 |
2007年 | 324篇 |
2006年 | 303篇 |
2005年 | 257篇 |
2004年 | 203篇 |
2003年 | 202篇 |
2002年 | 161篇 |
2001年 | 126篇 |
2000年 | 140篇 |
1999年 | 111篇 |
1998年 | 121篇 |
1997年 | 102篇 |
1996年 | 69篇 |
1995年 | 77篇 |
1994年 | 72篇 |
1993年 | 63篇 |
1992年 | 63篇 |
1991年 | 37篇 |
1990年 | 35篇 |
1989年 | 25篇 |
1988年 | 21篇 |
1987年 | 13篇 |
1986年 | 8篇 |
1985年 | 12篇 |
1984年 | 6篇 |
1983年 | 9篇 |
1982年 | 10篇 |
1981年 | 4篇 |
1980年 | 3篇 |
1979年 | 8篇 |
1978年 | 3篇 |
1971年 | 4篇 |
1969年 | 1篇 |
1957年 | 6篇 |
排序方式: 共有6879条查询结果,搜索用时 15 毫秒
51.
This study was aimed at providing new insights on the proteomic response of bacterial spores to ultrasound. Data-independent-acquisition method was used to quantify the proteome change of Bacillus cereus spores after ultrasound treatment (200 W). This study revealed that 2485 proteins were extracted from Bacillus cereus spores, most of them were related to metabolism. After ultrasound treatment, the expression of 340 proteins were significantly changed (the fold change ≥ 2 and p < 0.05), of which 207 proteins were significantly down-regulated. KEGG pathway analysis showed that differentially expressed proteins mainly distributed in metabolism pathway, cell process pathway and genetic information processing pathway after ultrasound treatment. Furthermore, this study analyzed the differentially expressed proteins in significant enrichment pathways. In particular, the expression of key proteins in the phosphorylation reaction of spores was significantly decreased after ultrasound treatment. Thus, ATP synthesis rate decreased and the phosphorylation reaction inhibited. Also, the decrease of the expression of key proteins related to the tricarboxylic acid cycle led to the decrease of nutrients metabolism of spores. Ultrasound treatment induced the down-regulation of fatty acid synthetase expression and promoted fatty acid metabolism at the same time. The content of fatty acids decreased in spores consequently. 相似文献
52.
Ultrafast transverse thermoelectric voltage response has been observed in c‐axis inclined epitaxial La0.5Sr0.5CoO3thin films. Voltage signals with the rise time of 7 ns have been detected under the irradiation of pulse laser with duration of 28 ns. A concept, named response rate ratio, has been proposed to evaluate the intrinsic response rate, and this ratio in La0.5Sr0.5CoO3is smaller than that in other reported materials. The low resistivity is thought to be responsible for the ultrafast response, as low resistivity induces small optical penetration depth, and response time has a monotonous increasing relationship with this depth.
53.
54.
55.
56.
The influence of the tuning of the radiation frequency of quantum-well heterolasers within the limits of their amplification
band on the output laser radiation parameters at different frequencies of pump-current modulation has been numerically simulated
using two optical models of an active medium under the assumption that the excess of the invariable component of the pump
current over its threshold value at any point of the amplification band is constant. It has been established that the amplitude-detuning
characteristics of the lasers studied are linear at high current-modulation frequencies and nonlinear at medium ones. The
behavior of the nonlinear spectral response of a laser diode is explained by its multiresonance structure and is mainly determined
by the ratio between the pump-current modulation frequency and the maximum resonance frequency of the laser.
__________
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 72, No. 4, pp. 473–478, July–August, 2005. 相似文献
57.
A. Pérez-González J. M. Vilar-Fernández W. González-Manteiga 《Annals of the Institute of Statistical Mathematics》2009,61(1):85-109
The main objective of this work is the nonparametric estimation of the regression function with correlated errors when observations
are missing in the response variable. Two nonparametric estimators of the regression function are proposed. The asymptotic
properties of these estimators are studied; expresions for the bias and the variance are obtained and the joint asymptotic
normality is established. A simulation study is also included. 相似文献
58.
59.
In this paper,using a fixed point theorem for condensing multi-valued maps,we investigate the existence of integral solutions to a class of nondensely defined neutral evolution impulsive differential inclusions with nonlocal conditions in Banach spaces. 相似文献
60.
Although event-related fMRI is able to reliably detect brief changes in brain activity and is now widely used throughout systems and cognitive neuroscience, there have been no previous reports of event-related spinal cord fMRI. This is likely attributable to the various technical challenges associated with spinal fMRI (e.g., imaging a suitable length of the cord, reducing image artifacts from the vertebrae and intervertebral discs, and dealing with physiological noise from spinal cord motion). However, with many of these issues now resolved, the largest remaining impediment for event-related spinal fMRI is a deprived understanding of the spinal cord fMRI signal time course. Therefore, in this study, we used a proton density-weighted HASTE sequence, with functional contrast based on signal enhancement by extravascular water protons (SEEP), and a motion-compensating GLM analysis to (i) characterize the SEEP response function in the human cervical spinal cord and (ii) demonstrate the feasibility of event-related spinal fMRI. This was achieved by applying very brief (1 s) epochs of 22°C thermal stimulation to the palm of the hand and measuring the impulse response function. Our results suggest that the spinal cord SEEP response (time to peak ≈8 s; FWHM ≈4 s; and probably lacking pre- and poststimulus undershoots) is slower than previous estimates of SEEP or BOLD responses in the brain, but faster than previously reported spinal cord BOLD responses. Finally, by detecting and mapping consistent signal-intensity changes within and across subjects, and validating these regions with a block-designed experiment, this study represents the first successful demonstration of event-related spinal fMRI. 相似文献