全文获取类型
收费全文 | 9007篇 |
免费 | 595篇 |
国内免费 | 21篇 |
专业分类
电工技术 | 125篇 |
综合类 | 18篇 |
化学工业 | 2339篇 |
金属工艺 | 170篇 |
机械仪表 | 207篇 |
建筑科学 | 321篇 |
矿业工程 | 36篇 |
能源动力 | 223篇 |
轻工业 | 402篇 |
水利工程 | 68篇 |
石油天然气 | 28篇 |
无线电 | 758篇 |
一般工业技术 | 2286篇 |
冶金工业 | 981篇 |
原子能技术 | 78篇 |
自动化技术 | 1583篇 |
出版年
2023年 | 153篇 |
2022年 | 374篇 |
2021年 | 418篇 |
2020年 | 285篇 |
2019年 | 246篇 |
2018年 | 301篇 |
2017年 | 255篇 |
2016年 | 349篇 |
2015年 | 297篇 |
2014年 | 438篇 |
2013年 | 550篇 |
2012年 | 547篇 |
2011年 | 623篇 |
2010年 | 423篇 |
2009年 | 412篇 |
2008年 | 433篇 |
2007年 | 416篇 |
2006年 | 324篇 |
2005年 | 252篇 |
2004年 | 222篇 |
2003年 | 201篇 |
2002年 | 191篇 |
2001年 | 122篇 |
2000年 | 113篇 |
1999年 | 119篇 |
1998年 | 193篇 |
1997年 | 154篇 |
1996年 | 105篇 |
1995年 | 83篇 |
1994年 | 73篇 |
1993年 | 90篇 |
1992年 | 53篇 |
1991年 | 50篇 |
1990年 | 50篇 |
1989年 | 37篇 |
1988年 | 44篇 |
1987年 | 40篇 |
1986年 | 34篇 |
1985年 | 42篇 |
1984年 | 37篇 |
1983年 | 32篇 |
1982年 | 27篇 |
1981年 | 27篇 |
1980年 | 23篇 |
1979年 | 19篇 |
1978年 | 28篇 |
1977年 | 24篇 |
1976年 | 60篇 |
1975年 | 27篇 |
1971年 | 17篇 |
排序方式: 共有9623条查询结果,搜索用时 15 毫秒
61.
Alexander Gatch Dimitry Gorsky Zy Biesinger Eric Bruestle Kelley Lee Curt Karboski Meredith L. Bartron Tyler Wagner 《Journal of Great Lakes research》2021,47(2):486-493
Restoration of a wild-produced lake trout Salvelinus namaycush population in Lake Ontario has not been successful despite the adult population often meeting or exceeding restoration targets. Lack of high-quality spawning habitat in Lake Ontario is suggested as one impediment to recruitment of wild lake trout, although the quantity and location of spawning habitat is poorly understood. If high-quality spawning habitat is limited in Lake Ontario, lake trout may be using uncommon spawning locations such as rivers. Anecdotal angler accounts point to the Niagara River as a lake trout spawning location. To better understand the potential of the Niagara River as a spawning location, egg and juvenile fish collections were conducted 12–14 river kilometers from the mouth of the Niagara River from 2010 to 2012; and mature female lake trout with surgically implanted acoustic tags were monitored from 2015 to 2019. Genetic analyses confirmed 60% of collected eggs and 93% of collected post-hatch juvenile fish in the Niagara River were lake trout. Tagged female lake trout returned to the Niagara River over consecutive years during the spawning season. The short duration of lake trout presence in the river (mean = 56 days/year) suggests female lake trout use the Niagara River primarily for spawning. Diversity in spawning locations may provide lake trout population’s resilience against environmental variability through a portfolio effect. Improved identification of riverine spawning locations, including their overall contribution to wild recruitment, may be a useful tool for managers to restore a wild-produced population of lake trout in Lake Ontario. 相似文献
62.
In this paper, a novel stochastic method is developed for despeckling transrectal ultrasound (TRUS) images of the prostate. By incorporating the circular probe acquisition particularities and speckle noise statistics of TRUS images of the prostate into a likelihood-weighted Monte Carlo estimation scheme, the proposed method can better remove speckle noise while preserving image structures and details that are relevant for image screening, allowing for a better delineation of the lesion contour. Our in silico and in vivo experimental results are promising, which was confirmed by a clinical evaluation of the in vivo test cases by experienced clinicians, and indicate that our method potentially can perform better than other previously proposed methods. 相似文献
63.
64.
In this paper we study small depth circuits that contain threshold gates (with or without weights) and parity gates. All circuits we consider are of polynomial size. We prove several results which complete the work on characterizing possible inclusions between many classes defined by small depth circuits. These results are the following:
相似文献
1. | A single threshold gate with weights cannot in general be replaced by a polynomial fan-in unweighted threshold gate of parity gates. |
2. | On the other hand it can be replaced by a depth 2 unweighted threshold circuit of polynomial size. An extension of this construction is used to prove that whatever can be computed by a depthd polynomial size threshold circuit with weights can be computed by a depthd+1 polynomial size unweighted threshold circuit, whered is an arbitrary fixed integer. |
3. | A polynomial fan-in threshold gate (with weights) of parity gates cannot in general be replaced by a depth 2 unweighted threshold circuit of polynomial size. |
65.
66.
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
67.
The Kirchhoff approximation is used to show that the time domain impulse response of an isolated flat crack can be given a simple geometrical interpretation in terms of the derivative of a projected length function. For an elliptical crack, this derivative can be obtained explicitly to yield the two edge-diffracted waves which originate from the flashpoints of the crack. An explicit coordinate invariant expression is obtained from this elliptical crack solution which relates the time difference, t, between the arrival of these edge-diffracted waves and the crack size and orientation. Previously, we have proposed that this expression, together with t measurements in different scattering directions, could be used in a regression analysis as the basis for performing a constrained inversion of crack scattering data (i.e., where we attempt to obtain the best equivalent flat elliptical crack that fits the scattering measurements). Here we will demonstrate some results of applying the proposed algorithm using noisy synthetic data. The sensitivity of the results to both, number of measurements and transducer orientation, will be discussed. 相似文献
68.
Alexander L. Fetter 《Journal of Low Temperature Physics》1987,67(1-2):17-25
A variational technique is used to analyze the deformed texture of superfluid3He-A in a narrow slab subject to a perpendicular magnetic field. Specific predictions are made for the anisotropy parameters
and
, averaged across the width. 相似文献
69.
Marie Burns Lennard Ostendorf Robert Biesen Andreas Grützkau Falk Hiepe Henrik E. Mei Tobias Alexander 《International journal of molecular sciences》2021,22(5)
Given its uniformly high expression on plasma cells, CD38 has been considered as a therapeutic target in patients with systemic lupus erythematosus (SLE). Herein, we investigate the distribution of CD38 expression by peripheral blood leukocyte lineages to evaluate the potential therapeutic effect of CD38-targeting antibodies on these immune cell subsets and to delineate the use of CD38 as a biomarker in SLE. We analyzed the expression of CD38 on peripheral blood leukocyte subsets by flow and mass cytometry in two different cohorts, comprising a total of 56 SLE patients. The CD38 expression levels were subsequently correlated across immune cell lineages and subsets, and with clinical and serologic disease parameters of SLE. Compared to healthy controls (HC), CD38 expression levels in SLE were significantly increased on circulating plasmacytoid dendritic cells, CD14++CD16+ monocytes, CD56+ CD16dim natural killer cells, marginal zone-like IgD+CD27+ B cells, and on CD4+ and CD8+ memory T cells. Correlation analyses revealed coordinated CD38 expression between individual innate and memory T cell subsets in SLE but not HC. However, CD38 expression levels were heterogeneous across patients, and no correlation was found between CD38 expression on immune cell subsets and the disease activity index SLEDAI-2K or established serologic and immunological markers of disease activity. In conclusion, we identified widespread changes in CD38 expression on SLE immune cells that highly correlated over different leukocyte subsets within individual patients, but was heterogenous within the population of SLE patients, regardless of disease severity or clinical manifestations. As anti-CD38 treatment is being investigated in SLE, our results may have important implications for the personalized targeting of pathogenic leukocytes by anti-CD38 monoclonal antibodies. 相似文献
70.
Alexander Kutschera Ursula Schombel Dominik Schwudke Stefanie Ranf Nicolas Gisch 《International journal of molecular sciences》2021,22(6)
Lipopolysaccharide (LPS), the major component of the outer membrane of Gram-negative bacteria, is important for bacterial viability in general and host–pathogen interactions in particular. Negative charges at its core oligosaccharide (core-OS) contribute to membrane integrity through bridging interactions with divalent cations. The molecular structure and synthesis of the core-OS have been resolved in various bacteria including the mammalian pathogen Pseudomonas aeruginosa. A few core-OS structures of plant-associated Pseudomonas strains have been solved to date, but the genetic components of the underlying biosynthesis remained unclear. We conducted a comparative genome analysis of the core-OS gene cluster in Pseudomonas syringae pv. tomato (Pst) DC3000, a widely used model pathogen in plant–microbe interactions, within the P. syringae species complex and to other plant-associated Pseudomonas strains. Our results suggest a genetic and structural conservation of the inner core-OS but variation in outer core-OS composition within the P. syringae species complex. Structural analysis of the core-OS of Pst DC3000 shows an uncommonly high phosphorylation and presence of an O-acetylated sugar. Finally, we combined the results of our genomic survey with available structure information to estimate the core-OS composition of other Pseudomonas species. 相似文献