全文获取类型
收费全文 | 12583篇 |
免费 | 400篇 |
国内免费 | 42篇 |
专业分类
电工技术 | 146篇 |
综合类 | 25篇 |
化学工业 | 2707篇 |
金属工艺 | 200篇 |
机械仪表 | 270篇 |
建筑科学 | 709篇 |
矿业工程 | 51篇 |
能源动力 | 200篇 |
轻工业 | 1174篇 |
水利工程 | 91篇 |
石油天然气 | 41篇 |
武器工业 | 1篇 |
无线电 | 725篇 |
一般工业技术 | 1853篇 |
冶金工业 | 2909篇 |
原子能技术 | 79篇 |
自动化技术 | 1844篇 |
出版年
2023年 | 74篇 |
2022年 | 177篇 |
2021年 | 201篇 |
2020年 | 140篇 |
2019年 | 159篇 |
2018年 | 224篇 |
2017年 | 165篇 |
2016年 | 246篇 |
2015年 | 236篇 |
2014年 | 317篇 |
2013年 | 731篇 |
2012年 | 524篇 |
2011年 | 742篇 |
2010年 | 532篇 |
2009年 | 536篇 |
2008年 | 574篇 |
2007年 | 583篇 |
2006年 | 497篇 |
2005年 | 431篇 |
2004年 | 398篇 |
2003年 | 326篇 |
2002年 | 329篇 |
2001年 | 234篇 |
2000年 | 234篇 |
1999年 | 224篇 |
1998年 | 313篇 |
1997年 | 272篇 |
1996年 | 241篇 |
1995年 | 203篇 |
1994年 | 188篇 |
1993年 | 221篇 |
1992年 | 210篇 |
1991年 | 110篇 |
1990年 | 161篇 |
1989年 | 150篇 |
1988年 | 145篇 |
1987年 | 129篇 |
1986年 | 112篇 |
1985年 | 143篇 |
1984年 | 133篇 |
1983年 | 103篇 |
1982年 | 98篇 |
1981年 | 118篇 |
1980年 | 98篇 |
1979年 | 116篇 |
1978年 | 84篇 |
1977年 | 92篇 |
1976年 | 70篇 |
1975年 | 81篇 |
1973年 | 65篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
Monroe William S. Skidmore Frank M. Odaibo David G. Tanik Murat M. 《Neural computing & applications》2021,33(11):6027-6038
Neural Computing and Applications - In the medical imaging domain, nonlinear warping has enabled pixel-by-pixel mapping of one image dataset to a reference dataset. This co-registration of data... 相似文献
72.
Phan Alex Truong Phuong Schade Christoph Vasan Aditya Friend James Talke Frank E. 《Microsystem Technologies》2021,27(6):2473-2479
Microsystem Technologies - “Zero drift” behavior of an optical intraocular pressure sensor is studied using an analytical model based on the deflection of a circular membrane. Results... 相似文献
73.
Certain tasks, such as formal program development and theorem proving, fundamentally rely upon the manipulation of higher-order objects such as functions and predicates. Computing tools intended to assist in performing these tasks are at present inadequate in both the amount of knowledge they contain (i.e., the level of support they provide) and in their ability to learn (i.e., their capacity to enhance that support over time). The application of a relevant machine learning technique—explanation-based generalization (EBG)—has thus far been limited to first-order problem representations. We extend EBG to generalize higher-order values, thereby enabling its application to higher-order problem encodings.Logic programming provides a uniform framework in which all aspects of explanation-based generalization and learning may be defined and carried out. First-order Horn logics (e.g., Prolog) are not, however, well suited to higher-order applications. Instead, we employ Prolog, a higher-order logic programming language, as our basic framework for realizing higher-order EBG. In order to capture the distinction between domain theory and training instance upon which EBG relies, we extend Prolog with the necessity operator of modal logic. We develop a meta-interpreter realizing EBG for the extended language, Prolog, and provide examples of higher-order EBG. 相似文献
74.
Conventional access methods cannot be effectively used in large Scientific/Statistical Database (SSDB) applications. A file structure (called bit transposed file (BTF)) is proposed which offers several attractive features that are better suited for the special characteristics that SSDBs exhibit. This file structure is an extreme version of the (attribute) transposed file. The data are stored by vertical bit partitions. The bit patterns of attributes are assigned using one of several data encoding methods. Each of these encoding methods is appropriate for different query types. The bit partitions can also be compressed using a version of the run length encoding scheme. Efficient operators on compressed bit vectors have been developed and form the basis of a query language. Because of the simplicity of the file structure and query language, optimization problems for database design, query evaluation, and common subexpression removal can be formalized and efficient exact solution or near optimal solution can be achieved. In addition to selective power with low overheads for SSDBs, the BTF is also amenable to special parallel hardware. Results from experiments with the file structure suggest that this approach may be a reasonable alternative file structure for large SSDBs. 相似文献
75.
Asymmetrically cracked specimens fail with considerably less ductility than symmetrically cracked ones, due to the crack progressing along a shear band into pre-damaged material. A formulation for the accumulation of damage ahead of an asymmetric crack is presented, based on strain increments following a power law relation. These results are integrated both numerically and approximately.The crack growth per unit displacement increases approximately as the logarithm of the total crack advance per inclusion spacing , and varies inversely as the critical fracture strain c. This provides a basis for predicting large-scale, fully plastic fracture from asymmetric weld defects, using small-scale laboratory specimens.
Résumé Les éprouvettes fissurées de manière asymétrique se rompent avec beaucoup moins de ductilité que celles qui sont fissurées de manières symétrique, en raison du fait que la fissure se développe suivant une bande de cisaillement dans un matériau préendommagé. On Présente une formulation de l'accumulation du dommage en avant d'une fissure asymétrique, en se basant sur des gradients de déformations répartis selon une loi quadratique. L'interprétation des résultats est effectuée par voie numérique et par approximation.On constate que le croissance d'une fissure par unité de déplacement est sensiblement proportionnelle au logarithme de l'avancement total de la fissure rapporté à l'espacement entre deux inclusions , et en raison inverse de la déformation critique à la rupture c. Ceci fournt une base pour prédire une rupture à plus grande échelle et en conditions tout à fait plastiques, qui résulteront de défauts de soudage asymétriques, et ce en utilisant des éprouvettes réduites de laboratoire.相似文献
76.
Natasha M. van Poppelen Jolique A. van Ipenburg Quincy van den Bosch Jolanda Vaarwater Tom Brands Bert Eussen Frank Magielsen Hendrikus J. Dubbink Dion Paridaens Erwin Brosens Nicole Naus Annelies de Klein Emine Kili Robert M. Verdijk 《International journal of molecular sciences》2021,22(11)
The aim of this study was exploration of the genetic background of conjunctival melanoma (CM) and correlation with recurrent and metastatic disease. Twenty-eight CM from the Rotterdam Ocular Melanoma Study group were collected and DNA was isolated from the formalin-fixed paraffin embedded tissue. Targeted next-generation sequencing was performed using a panel covering GNAQ, GNA11, EIF1AX, BAP1, BRAF, NRAS, c-KIT, PTEN, SF3B1, and TERT genes. Recurrences and metastasis were present in eight (29%) and nine (32%) CM cases, respectively. TERT promoter mutations were most common (54%), but BRAF (46%), NRAS (21%), BAP1 (18%), PTEN (14%), c-KIT (7%), and SF3B1 (4%) mutations were also observed. No mutations in GNAQ, GNA11, and EIF1AX were found. None of the mutations was significantly associated with recurrent disease. Presence of a TERT promoter mutation was associated with metastatic disease (p-value = 0.008). Based on our molecular findings, CM comprises a separate entity within melanoma, although there are overlapping molecular features with uveal melanoma, such as the presence of BAP1 and SF3B1 mutations. This warrants careful interpretation of molecular data, in the light of clinical findings. About three quarter of CM contain drug-targetable mutations, and TERT promoter mutations are correlated to metastatic disease in CM. 相似文献
77.
KeShun Liu Frank Orthoefer Edward A. Brown 《Journal of the American Oil Chemists' Society》1995,72(2):189-192
Ten soybean genotypes grown in 1992 with seed size ranging from 7.6 to 30.3 g/100 seeds and maturity group V or VI were selected
and tested for oil and protein content and for fatty acid composition. In these germplasm, protein varied from 39.5 to 50.2%,
oil, 16.3 to 21.6%, and protein plus oil, 59.7 to 67.5%. Percentages of individual fatty acids relative to total fatty acids
varied as follows: palmitic, 11.0 to 12.8; stearic, 3.2 to 4.7; oleic, 17.6 to 24.2; linoleic, 51.1 to 56.3 and linolenic,
6.9 to 10.0. Seed size showed no significant correlations with individual saturated fatty acids, protein or oil content. However,
significant correlations were found between seed size and individual unsaturated fatty acids: positive with oleic, and negative
with linoleic and linolenic. Oil and protein content were negatively correlated with each other. Among the major fatty acids,
only the unsaturated were significantly correlated with each other: negative between oleic and linoleic or linolenic, and
positive between linoleic and linolenic. A subsequent study with soybeans grown in 1993 generally confirmed these findings.
Variation in relative percentages of unsaturated fatty acids andr values for most pairs of relationships were even higher than those obtained from the 1992 crop.
Presented at the 85th AOCS Annual Meeting and Expo, Atlanta, Georgia, May 8–12, 1994. 相似文献
78.
Fish oils containing different levels of polymers of triacylglycerols formed during autoxidation were incubated with pancreatic
lipase to establish whether these polymers are substrates for lipase hydrolysis. With oils containing low amounts (less than
4%) of triacylglycerol polymers as substrates, both triacylglycerols and polymers of triacylglycerols were almost completely
hydrolyzed, and fatty acid monomers and monoacylglycerols were the major lipid products. Under the same incubation conditions,
some triacylglycerols remained intact when highly oxidized oils containing 20 or 30% triacylglycerol polymers were the substrate.
The fatty acid composition of these residual triacylglycerols was almost identical to that of triacylglycerols present at
the start of the assay. When fish oil containing 30% triacylglycerol polymers was incubated with the lipase, the component
triacylglycerols and polymers of triacylglycerols were hydrolyzed at similar rates, and fatty acid dimers were detected as
a product. It is concluded that the high molecular weight polymers of triacylglycerols present in oxidized fish oils can be
hydrolyzed by pancreatic lipasein vitro. 相似文献
79.
Summary Asparagus seed, Mary Washington variety, was found to contain 14.7% of glyceride oil having iodine value 135.1, saponification
value 185.5, and unsaponifiable matter 1.46%. The oil was converted to methyl esters, and the mixed esters were separated
by fractional distillation and low-temperature crystallization. The acids were identified by chemical and physical methods.
The % composition of the fatty acids is estimated from the data as follows: palmitic 3, linoleic 57, oleic 27, stearic 2,
eicosenoic 1.5, arachidic 0.6, undetermined 9. The oil is somewhat similar to corn oil in composition. It has at least 2%
of acids of the C20 series, which have not been reported previously in this plant family (Liliaceae).
Presented at the meeting of the American Oil Chemists' Society, Philadelphia, Pa., October 10–12, 1955. Issued as N.R.C. No.
4426. 相似文献
80.