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941.
942.
Crone B Dodabalapur A Lin YY Filas RW Bao Z LaDuca A Sarpeshkar R Katz HE Li W 《Nature》2000,403(6769):521-523
Thin-film transistors based on molecular and polymeric organic materials have been proposed for a number of applications, such as displays and radio-frequency identification tags. The main factors motivating investigations of organic transistors are their lower cost and simpler packaging, relative to conventional inorganic electronics, and their compatibility with flexible substrates. In most digital circuitry, minimal power dissipation and stability of performance against transistor parameter variations are crucial. In silicon-based microelectronics, these are achieved through the use of complementary logic-which incorporates both p- and n-type transistors-and it is therefore reasonable to suppose that adoption of such an approach with organic semiconductors will similarly result in reduced power dissipation, improved noise margins and greater operational stability. Complementary inverters and ring oscillators have already been reported. Here we show that such an approach can realize much larger scales of integration (in the present case, up to 864 transistors per circuit) and operation speeds of approximately 1 kHz in clocked sequential complementary circuits. 相似文献
943.
Free radicals in biological materials 总被引:11,自引:0,他引:11
944.
945.
引言本文目的是要分析建立引力论所依据的原理,換言之,是要分析这一理論的邏輯結构。今天看来,相对论和引力論都成了經典的东西了,但是直到目前为止,对于它們——尤其是对引力論——有时还有些不正确的观念,因而也形成了一些不正确的术语。反之,已经建立起来的不正确术语又使不正确的观念得以保存。因此,术語問题不是一个簡单的形式上的問题,而必須对它加以注意。从这观点出发,下面首先要考察“广义的相对性”和“广义相对論”这两个术語。后者一般是指爱因斯坦的引力論而言。这些术語是爱因斯坦本人引进的,它們反映着他对自己創立的理論的观点。下面簡单介紹一下这些观点。 相似文献
946.
947.
The breakdown of continuum models for mechanical contacts 总被引:5,自引:0,他引:5
Forces acting within the area of atomic contact between surfaces play a central role in friction and adhesion. Such forces are traditionally calculated using continuum contact mechanics, which is known to break down as the contact radius approaches atomic dimensions. Yet contact mechanics is being applied at ever smaller lengths, driven by interest in shrinking devices to nanometre scales, creating nanostructured materials with optimized mechanical properties, and understanding the molecular origins of macroscopic friction and adhesion. Here we use molecular simulations to test the limits of contact mechanics under ideal conditions. Our findings indicate that atomic discreteness within the bulk of the solids does not have a significant effect, but that the atomic-scale surface roughness that is always produced by discrete atoms leads to dramatic deviations from continuum theory. Contact areas and stresses may be changed by a factor of two, whereas friction and lateral contact stiffness change by an order of magnitude. These variations are likely to affect continuum predictions for many macroscopic rough surfaces, where studies show that the total contact area is broken up into many separate regions with very small mean radius. 相似文献
948.
Until now, the analysis of burrowing mechanics has neglected the mechanical properties of impeding, muddy, cohesive sediments, which behave like elastic solids. Here we show that burrowers can progress through such sediments by using a mechanically efficient, previously unsuspected mechanism--crack propagation--in which an alternating 'anchor' system of burrowing serves as a wedge to extend the crack-shaped burrow. The force required to propagate cracks through sediment in this way is relatively small: we find that the force exerted by the annelid worm Nereis virens in making and moving into such a burrow amounts to less than one-tenth of the force it needs to use against rigid aquarium walls. 相似文献
949.
A high-resolution map of active promoters in the human genome 总被引:1,自引:0,他引:1
Kim TH Barrera LO Zheng M Qu C Singer MA Richmond TA Wu Y Green RD Ren B 《Nature》2005,436(7052):876-880
950.
Gunsalus KC Ge H Schetter AJ Goldberg DS Han JD Hao T Berriz GF Bertin N Huang J Chuang LS Li N Mani R Hyman AA Sönnichsen B Echeverri CJ Roth FP Vidal M Piano F 《Nature》2005,436(7052):861-865
Although numerous fundamental aspects of development have been uncovered through the study of individual genes and proteins, system-level models are still missing for most developmental processes. The first two cell divisions of Caenorhabditis elegans embryogenesis constitute an ideal test bed for a system-level approach. Early embryogenesis, including processes such as cell division and establishment of cellular polarity, is readily amenable to large-scale functional analysis. A first step toward a system-level understanding is to provide 'first-draft' models both of the molecular assemblies involved and of the functional connections between them. Here we show that such models can be derived from an integrated gene/protein network generated from three different types of functional relationship: protein interaction, expression profiling similarity and phenotypic profiling similarity, as estimated from detailed early embryonic RNA interference phenotypes systematically recorded for hundreds of early embryogenesis genes. The topology of the integrated network suggests that C. elegans early embryogenesis is achieved through coordination of a limited set of molecular machines. We assessed the overall predictive value of such molecular machine models by dynamic localization of ten previously uncharacterized proteins within the living embryo. 相似文献