全文获取类型
收费全文 | 225393篇 |
免费 | 2219篇 |
国内免费 | 708篇 |
专业分类
化学 | 107677篇 |
晶体学 | 3292篇 |
力学 | 7814篇 |
综合类 | 4篇 |
数学 | 18341篇 |
物理学 | 60157篇 |
无线电 | 31035篇 |
出版年
2016年 | 2502篇 |
2015年 | 1795篇 |
2014年 | 2633篇 |
2013年 | 8302篇 |
2012年 | 5565篇 |
2011年 | 6962篇 |
2010年 | 4931篇 |
2009年 | 5166篇 |
2008年 | 7033篇 |
2007年 | 7528篇 |
2006年 | 7309篇 |
2005年 | 6730篇 |
2004年 | 6172篇 |
2003年 | 5577篇 |
2002年 | 5487篇 |
2001年 | 7027篇 |
2000年 | 5575篇 |
1999年 | 4573篇 |
1998年 | 3795篇 |
1997年 | 3825篇 |
1996年 | 3727篇 |
1995年 | 3455篇 |
1994年 | 3327篇 |
1993年 | 3212篇 |
1992年 | 3710篇 |
1991年 | 3603篇 |
1990年 | 3414篇 |
1989年 | 3438篇 |
1988年 | 3291篇 |
1987年 | 2932篇 |
1986年 | 2756篇 |
1985年 | 3633篇 |
1984年 | 3653篇 |
1983年 | 3069篇 |
1982年 | 3211篇 |
1981年 | 3146篇 |
1980年 | 3007篇 |
1979年 | 3112篇 |
1978年 | 3353篇 |
1977年 | 3142篇 |
1976年 | 3109篇 |
1975年 | 2926篇 |
1974年 | 2870篇 |
1973年 | 2897篇 |
1972年 | 1896篇 |
1971年 | 1606篇 |
1968年 | 2038篇 |
1967年 | 2209篇 |
1966年 | 2017篇 |
1965年 | 1580篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
M Lepère R Gobeille V.Malathy Devi M.A.H Smith B Aoaeh A.W Mantz 《Journal of Molecular Spectroscopy》2004,224(1):7-12
We have analyzed the methyl fluoride RQ(J,0)Q branch lines located near 1475 cm−1 using a simultaneous multi-spectrum fitting technique. In this analysis we have used previously recorded diode-laser data in which we collected many data points covering only one or two Q branch lines in a particular run. The analysis consists of simultaneously fitting 57 spectra collected with numerous pressure and path length conditions for all absorption lines. The data are concatenated to create one continuous spectrum of the Q branch. We have determined the intensity and self-broadened widths at 296 K for 23 RQ(J,0) lines. 相似文献
102.
A homologous series of azomesogens, 2″-[4-(4′-n-alkoxybenzoyloxy)-2-chlorophenylazo] naphthalenes, with lateral chloro groups was synthesised. All the homologues synthesized
exhibit enantiotropic nematic mesophase. The mesomorphic properties of the present series are compared with other structurally
related series to evaluate the effect of lateral chloro group and its position on mesomorphism
This paper was presented at the 10th National Conference on Liquid Crystals held at Bangalore, India during 9–11 October 2003. 相似文献
103.
We extend the matrix version of Cochran's statistical theorem to outer inverses of a matrix. As applications, we investigate the Wishartness and independence of matrix quadratic forms for Kronecker product covariance structures. 相似文献
104.
Summary Using a saturated non-boiling hydrocarbon mixture, the influence of two parameters on the results of field ionization mass spectrometry (FI-MS) measurements was studied: (a) the potential difference between the FI emitter and the counterelectrode; (b) the emitter temperature.Variation of the potential difference had only a minor effect on the average molecular mass measured and had no evident effect on the relative ring number distribution in the sample. In contrast, when the emitter temperature was increased, higher average molecular masses were recorded. Moreover, the average molecular masses shifted to higher ring numbers. In order to control the relationship between the described influences during mixture analysis, measuring instructions have been developed that enable the quantitative analysis of unknown saturated samples. However, average molecular mass of the mixture must be known.
Entwicklung einer quantitativen FI-MS-Methode zur Charakterisierung von gesättigten hoch- und nichtsiedenden Kohlenwasserstoffgemischen相似文献
105.
106.
A planar double-gate SOI MOSFET (DG-SOI) with thin channel and thick source/drain (S/D) was successfully fabricated. Using both experimental data and simulation results, the S/D asymmetric effect induced by gate misalignment was studied. For a misaligned DG-SOI, there is gate nonoverlapped region on one side and extra gate overlapped region on the other side. The nonoverlapped region introduces extra series resistance and weakly controlled channel, while the extra overlapped region introduces additional overlap capacitance and gate leakage current. We compared two cases: bottom gate shift to source side (DG/spl I.bar/S) and bottom gate shift to drain side (DG/spl I.bar/D). At the same gate misalignment value, DG/spl I.bar/S resulted in a larger drain-induced barrier lowering effect and smaller overlap capacitance at drain side than DG/spl I.bar/D. Because of reduced drain-side capacitance, the speed of three-stage ring oscillator of DG/spl I.bar/S, with 20% gate misalignment length (L/sub mis/) over gate length (L/sub g/), or L/sub mis//L/sub g/=20%, was faster than that of two-gate aligned DG-SOI. 相似文献
107.
Cogburn D.L. Mueller M. McKnight L. Klein H. Mathiason J. 《Communications Magazine, IEEE》2005,43(12):12-14
Who should control the Internet? A dozen years after the Internet became a mass medium, this issue has continued to grow in urgency, becoming white hot in fall 2005. At the September 2005 preparatory meeting for the UN World Summit on the Information Society (WSIS), a coalition of countries criticized the United States' unilateral control of the Internet's domain name system (DNS) and proposed the establishment of a multinational Council to supervise it. This proposal emerged from the Final Report of the UN Working Group on Internet Governance. Researchers from the Internet Governance Project, a university-based consortium for policy analysis, have concluded that the United States should internationalize governance of the Internet, but in a way that avoids intrusive, centralized control. 相似文献
108.
H E Cline W E Lorensen R J Herfkens G A Johnson G H Glover 《Magnetic resonance imaging》1989,7(1):45-54
A three-dimensional examination of blood vessels is provided using MR data from seven cases. The vascular surfaces are constructed with an algorithm that automatically follows the selected artery or vein and generates a projected three-dimensional gradient shaded image. Fast 3DFT pulse sequences were optimized to enhance the time-of-flight contrast of the intravascular region. By increasing the surface threshold value in a three-dimensional head study, the flesh of a patient's face was peeled away to demonstrate the superfacial temporal artery. Gated cardiac images show the great vessels and cardiac chambers. A three-dimensional view of the aorta shows an irregular surface in the vicinity of an adrenal tumor. 3D MR exams provide a non-invasive technique for assessing vascular morphology in a clinical setting. 相似文献
109.
V. Vassilev S. Thijs P. L. Segura P. Wambacq P. Leroux G. Groeseneken M. I. Natarajan H. E. Maes M. Steyaert 《Microelectronics Reliability》2005,45(2):255-268
This paper describes an approach to design ESD protection for integrated low noise amplifier (LNA) circuits used in narrowband transceiver front-ends. The RF constraints on the implementation of ESD protection devices are relaxed by co-designing the RF and the ESD blocks, considering them as one single circuit to optimise. The method is applied for the design of 0.25 μm CMOS LNA. Circuit protection levels higher than 3 kV HBM stress are achieved using conventional highly capacitive ggNMOS snapback devices. The methodology can be extended to other RF-CMOS circuits requiring ESD protection by merging the ESD devices in the functionality of the corresponding matching blocks. 相似文献
110.
A novel finger‐sensing nanocomposite with remarkable and reversible piezoresistivity is successfully fabricated by dispersing homogeneously conductive graphite nanosheets (GNs) in a silicone rubber (SR) matrix. Because of the high aspect ratio of the graphite nanosheets, the nanocomposite displays a very low percolation threshold. The SR/GN nanocomposite with a volume fraction of conductive nanosheets closest to that for the percolation threshold presents a sharp positive‐pressure coefficient effect of the resistivity under very low pressure, namely, in the finger‐pressure range (0.3–0.7 MPa), whereby the abrupt transition could be attributed to compressive‐stress‐induced deformation of the conducting network. The super‐sensitive piezoresistive behavior of the nanocomposite is accounted for by an extension of the tunneling conduction theory which provides a good approximation to the piezoresistive effect. 相似文献