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181.
Paul Beame Allan Borodin Prabhakar Raghavan Walter L. Ruzzo Martin Tompa 《Information and Computation》1996,130(2):101
We investigate time-space tradeoffs for traversing undirected graphs, using a variety of structured models that are all variants of Cook and Rackoff's “Jumping Automata for Graphs.” Our strongest tradeoff is a quadratic lower bound on the product of time and space for graph traversal. For example, achieving linear time requires linear space, implying that depth-first search is optimal. Since our bound in fact applies to nondeterministic algorithms fornonconnectivity, it also implies that closure under complementation of nondeterministic space-bounded complexity classes is achieved only at the expense of increased time. To demonstrate that these structured models are realistic, we also investigate their power. In addition to admitting well known algorithms such as depth-first search and random walk, we show that one simple variant of this model is nearly as powerful as a Turing machine. Specifically, for general undirected graph problems, it can simulate a Turing machine with only a constant factor increase in space and a polynomial factor increase in time. 相似文献
182.
Reviews the book, Meaningful differences in the everyday experience of young American children by Betty Hart and Todd R. Risley (1996). This volume, the first booklength report of a large-scale longitudinal study conducted by the authors at the Juniper Gardens Children's Project of the University of Kansas, describes language development, and the factors associated with this development, for young children living in different socioeconomic situations. Hart and Risley's book describes the methodology and initial results of their investigation, with a strong focus on the developmental outcomes and experiences of children from 12 to 36 months of age. Why should school psychologists, with a predominant and (in many ways) appropriate focus on school-aged children, turn to this volume? The answer, I think, lies in the story that these authors tell, and in the lessons that we can learn from the way this story is told. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
183.
Ruth Onn Allan O. Steinhardt 《International Journal of Adaptive Control and Signal Processing》1993,7(2):103-116
The purpose of this paper is to elucidate the multi-window method for spectral estimation and sinusoid detection. The multi-window method, devised by D. J. Thomson, has many features that distinguish it from other spectrum estimation techniques. It has an elegant derivation, starting from first principles and using optimality arguments. It lends itself to performance analysis and provides a built-in measure of its reliability. In contrast to Thomson's integral equation derivation, we use linear algebraic methods both to treat the problem and to develop the solution. In addition to the tutorial, we present an overview of published generalizations and analyses of the method. 相似文献
184.
Karlene A. Kosanovich Allan R. Moser Michael J. Piovoso 《Chemical Engineering Communications》1996,146(1):131-138
This paper introduces a family of wavelet transforms based on the Poisson Transform. The wavelet transform maps L2 (R)functions to a space described by two continuous variables, scale and translation, as well as a discrete index. Reconstruction in the wavelet domain can be done for each of the discrete indices. Additionally, a different reconstruction formula exists for the Poisson Transform domain. We develop the Poisson Wavelet Transform, present an example relevant to stable, over-damped, linear, time-invariant systems, and show the relationship between the Poisson Transform and the Poisson Wavelet Transform. 相似文献
185.
IM Ahmed M Lagopoulos P McConnell RW Soames GK Sefton 《Canadian Metallurgical Quarterly》1998,16(5):591-596
The Escherichia coli low molecular mass penicillin-binding proteins are enzymes associated with the periplasmic face of the inner membrane. This mini review discusses the membrane anchoring of these enzymes and their possible participation in a putative membrane bound protein complex involved in the regulation of peptidoglycan biosynthesis. The identification of such a complex may lead to the identification of new sites of action for antibacterial compounds. 相似文献
186.
Melinda L Perkins Bruce R D'Arcy Allan T Lisle Hilton C Deeth 《Journal of the science of food and agriculture》2005,85(14):2421-2428
Solid phase microextraction (SPME) offers a solvent‐free and less labour‐intensive alternative to traditional flavour isolation techniques. In this instance, SPME was optimised for the extraction of 17 stale flavour volatiles (C3–11,13 methyl ketones and C4–10 saturated aldehydes) from the headspace of full‐cream ultrahigh‐temperature (UHT)‐processed milk. A comparison of relative extraction efficiencies was made using three fibre coatings, three extraction times and three extraction temperatures. Linearity of calibration curves, limits of detection and repeatability (coefficients of variation) were also used in determining the optimum extraction conditions. A 2 cm fibre coating of 50/30 µm divinylbenzene/Carboxen/polydimethylsiloxane in conjunction with a 15 min extraction at 40 °C were chosen as the final optimum conditions. This method can be used as an objective tool for monitoring the flavour quality of UHT milk during storage. Copyright © 2005 Society of Chemical Industry 相似文献
187.
Brain levels of glycerophosphodiesters, including glycerophosphocholine (GPC) and glycerophosphoethanolamine (GPE), are altered
in many human central nervous system disorders. Although much information is available on the enzymes responsible for the
formation of these phospholipid metabolites, little information is known regarding their catabolism, by glycerophosphodiesterases,
in human brain. In both autopsied and biopsied temporal cortex, a phosphocholine-producing lycerophosphodiesterase activity
was observed. In the presence of 1 mM EDTA, the enzyme possessed a pH optimum of 9.0, while the addition of 5 mM zinc acetate
shifted the pH optimum to 10.5. When assayed at pH 9.0 in the absence of zinc acetate, the Km and Vmax were 104±2 μM and 77±18 nmol/h/mg protein, respectively, while assaying at pH 10.5 in the presence of 5 mM zinc acetate yielded
a Km of 964±56 μM, and a Vmax of 534±114 nmol/h/mg protein. Furthermore, whereas submillimolar concentrations of zinc acetate stimulated the activity of
the enzyme in a dose-dependent manner when assayed at pH 10.5 (EC50=20.3±3.0 μM), this did not result in a reciprocal inhibition of glycerophosphocholine phosphodiesterase (GPC PD) activity
when assayed at a more acidic pH. This may suggest that human brain contains two phosphocholine-producing GPC PD activities,
differentiable by their sensitivity to zinc ions. An activity capable of hydrolyzing GPE to form phosphoethanolamine could
not be detected in either biopsied or autopsied brain. However, a choline/ethanolamine-producing glycerophosphodiesterase
activity could be readily detected in biopsied, but not autopsied brain. This novel enzyme possessed a neutral pH optimum
and was dependent upon divalent cations for activity. In conclusion, human brain contains at least two different glycerophosphodiesterases,
a phosphocholine, and a choline/ethanolamine-producing activity, only one of which can be detected in autopsied tissue. The
results of previous studies measuring brain glycerophosphodiesterase activity in degenerative brain conditions may need to
be reevaluated in the light of these observations. 相似文献
188.
Milan P. Allan Simon Berner Martina Corso Thomas Greber Jürg Osterwalder 《Nanoscale research letters》2007,2(2):94-99
High-temperature exposure of a Mo(110) surface to borazine (HBNH)3 leads to the formation of two distinctly different self-assembling nanostructures. Depending on the substrate temperature
during preparation, either well-aligned, ultra-thin boron nanowires or a single-layer stripe structure of hexagonal boron
nitride forms. Both structures show one-dimensional (1D) characteristics, but in directions perpendicular to each other. It
is also possible to grow the two phases in coexistence. The relative weights are controlled by the sample temperature during
preparation. 相似文献
189.
If you are a psychologist who conducts child custody or personal injury evaluations, how confident are you that the traditional Minnesota Multiphasic Personality Inventory—2nd ed. (MMPI—2) validity scales and other potential MMPI—2 validity indicators are in fact useful for addressing the issue of response bias? This investigation contributes to the scientific database on the use of MMPI—2 validity indicators to detect response distortion. As the investigation represents empirical rather than analog data, it is of particular value to psychologists who engage in forensic assessment. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
190.
怎样报导一个在柏林有五天会议和80场附加展览,以及全德国的7次预备会议好呢?在4000多名代表中,58%不是德国人,其中最大的代表团是来自巴西、中国、法国、希腊和俄国的,非洲和印度没有出席.为什么这样呢? 相似文献