全文获取类型
收费全文 | 4842篇 |
免费 | 256篇 |
国内免费 | 2篇 |
专业分类
电工技术 | 40篇 |
综合类 | 1篇 |
化学工业 | 918篇 |
金属工艺 | 34篇 |
机械仪表 | 49篇 |
建筑科学 | 167篇 |
矿业工程 | 9篇 |
能源动力 | 93篇 |
轻工业 | 561篇 |
水利工程 | 52篇 |
石油天然气 | 11篇 |
无线电 | 274篇 |
一般工业技术 | 749篇 |
冶金工业 | 1651篇 |
原子能技术 | 6篇 |
自动化技术 | 485篇 |
出版年
2023年 | 29篇 |
2022年 | 61篇 |
2021年 | 105篇 |
2020年 | 68篇 |
2019年 | 65篇 |
2018年 | 97篇 |
2017年 | 99篇 |
2016年 | 104篇 |
2015年 | 102篇 |
2014年 | 128篇 |
2013年 | 242篇 |
2012年 | 205篇 |
2011年 | 366篇 |
2010年 | 269篇 |
2009年 | 247篇 |
2008年 | 300篇 |
2007年 | 277篇 |
2006年 | 241篇 |
2005年 | 199篇 |
2004年 | 165篇 |
2003年 | 152篇 |
2002年 | 143篇 |
2001年 | 105篇 |
2000年 | 81篇 |
1999年 | 92篇 |
1998年 | 139篇 |
1997年 | 141篇 |
1996年 | 83篇 |
1995年 | 82篇 |
1994年 | 60篇 |
1993年 | 64篇 |
1992年 | 51篇 |
1991年 | 25篇 |
1990年 | 35篇 |
1989年 | 41篇 |
1988年 | 29篇 |
1987年 | 36篇 |
1986年 | 29篇 |
1985年 | 31篇 |
1984年 | 24篇 |
1983年 | 25篇 |
1982年 | 21篇 |
1981年 | 23篇 |
1980年 | 20篇 |
1979年 | 14篇 |
1978年 | 11篇 |
1977年 | 18篇 |
1976年 | 44篇 |
1975年 | 29篇 |
1974年 | 15篇 |
排序方式: 共有5100条查询结果,搜索用时 15 毫秒
101.
SR DeMeester GA Patterson RS Sundaresan JD Cooper 《Canadian Metallurgical Quarterly》1998,115(3):681-688
Methanol-induced conformational transitions of hen egg white lysozyme were investigated with a combined use of far- and near-UV CD and NMR spectroscopies, ANS binding and small-angle X-ray scattering. Addition of methanol induced no global change in the native conformation itself, but induced a transition from the native state to the denatured state which was highly cooperative, as shown by the coincidence of transition curves monitored by the far- and near-UV CD spectroscopy, by isodichroic points in the far- and near-UV CD spectra and by the concomitant disappearance of individual 1H NMR signals of the native state. The ANS binding experiments could detect no intermediate conformer similar to the molten globule state in the process of the methanol denaturation. However, at high concentration of methanol, e.g., 60% (v/v) methanol/water, a highly helical state (H) was realized. The H state had a helical content much higher than the native state, monitored by far-UV CD spectroscopy, and had no specific tertiary structure, monitored both by near-UV CD and NMR spectroscopy. The radius of gyration in the H state, 24.9 angstroms, was significantly larger than that in the native state (15.7 angstroms). The Kratky plot for the H state did not show a clear peak and was quite similar to that for the urea-denatured state, indicating a complete lack of globularity. Thus we conclude that the H state has a considerably expanded, flexible broken rod-like conformation which is clearly distinguishable from the "molten globule" state. The stability of both N and H states depends on pH and methanol concentration. Thus a phase diagram involving N and H was constructed. 相似文献
102.
Influence of layered tissue architecture on estimates of tissue optical properties obtained from spatially resolved diffuse reflectometry 总被引:2,自引:0,他引:2
Most instruments used to measure tissue optical properties noninvasively employ data-analysis algorithms that rely on the simplifying assumption that the tissue is semi-infinite and homogeneous. The influence of a layered tissue architecture on the determination of the scattering and absorption coefficients has been investigated in this study. Reflectance as a function of distance from a point source for a two-layered tissue architecture that simulates skin overlying fat was calculated by using a Monte Carlocode. These data were analyzed by using a diffusion theory modelfor a homogeneous semi-infinite medium to calculate the scatter and absorption coefficients. Depending on the algorithm and the radial distance, the estimated tissue optical properties were different from those of either layer, and under some circumstances, physically impossible. In addition, the sensitivity and cross talk of the estimated optical properties to changes in input optical properties were calculated for different layered geometries. For typical optical properties of skin, the sensitivity to changes in optical properties is highly dependent on the layered architecture, the measurement distance, and the fitting algorithm. Furthermore, a change in the input absorption coefficient may result in an apparent change in the measured scatter coefficient, and a change in the in put scatter coefficient may result in an apparent change in the measured absorption coefficient. 相似文献
103.
Laser Doppler measurements were performed on scattering liquids flowing through a highly scattering static medium to determine the scattering coefficient and the anisotropy factor of the liquids. Monte Carlo simulations of light propagation in the static and moving media were used to calculate the Doppler spectra for suspensions of polystyrene spheres in water, and these spectra were in excellent agreement with experimental results. A faster Monte Carlo code was developed so that nonlinear regressions to the measured laser Doppler spectra could be used to determine the anisotropy factor of other liquids. This approach was used to deduce the scattering properties of Intralipid and blood at λ = 820 nm. It was found that the anisotropy factor of blood is well described by Mie theory in contradiction to results reported in the literature that were obtained by goniometric measurement of the phase function. 相似文献
104.
Quinn Paul C.; Cummins Maggie; Kase Jennifer; Martin Erin; Weissman Sheri 《Canadian Metallurgical Quarterly》1996,32(5):942
A series of experiments examined the abilities of infants to form categorical representations for the spatial relations above and below. Exp 1 provided evidence that 3–4 mo olds can form categorical representations for above and below when a diamond shape was presented above or below a horizontal bar. Exps 2 and 3 showed that 3- and 4-mo olds did not form categorical representations for above and below when a number of discriminably different shapes (e.g., a diamond, a triangle, a dot) appeared above or below the bar. These more abstract categorical representations for above and below were formed by 6- to 7-mo olds (Exp 4). The findings suggest an experientially or maturationally based trend, from concrete to abstract, in the categorical representation of common spatial relations. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
105.
Verb Phrase Ellipsis (VPE) has been studied in great depth in theoretical linguistics, but empirical studies of VPE are rare.
We extend the few previous corpus studies with an annotated corpus of VPE in all 25 sections of the Wall Street Journal corpus
(WSJ) distributed with the Penn Treebank. We annotated the raw files using a stand-off annotation scheme that codes the auxiliary
verb triggering the elided verb phrase, the start and end of the antecedent, the syntactic type of antecedent (VP, TV, NP,
PP or AP), and the type of syntactic pattern between the source and target clauses of the VPE and its antecedent. We found
487 instances of VPE (including predicative ellipsis, antecedent-contained deletion, comparative constructions, and pseudo-gapping)
plus 67 cases of related phenomena such as do so anaphora. Inter-annotator agreement was high, with a 0.97 average F-score for three annotators for one section of the WSJ.
Our annotation is theory neutral, and has better coverage than earlier efforts that relied on automatic methods, e.g. simply
searching the parsed version of the Penn Treebank for empty VP’s achieves a high precision (0.95) but low recall (0.58) when
compared with our manual annotation. The distribution of VPE source–target patterns deviates highly from the standard examples
found in the theoretical linguistics literature on VPE, once more underlining the value of corpus studies. The resulting corpus
will be useful for studying VPE phenomena as well as for evaluating natural language processing systems equipped with ellipsis
resolution algorithms, and we propose evaluation measures for VPE detection and VPE antecedent selection. The stand-off annotation
is freely available for research purposes. 相似文献
106.
Carpenters and other construction workers who install drywall have high rates of strains and sprains to the low back and shoulder. Drywall is heavy and awkward to handle resulting in increased risk of injury. The purpose of this study was to evaluate several low-cost coupling tools that have the potential to reduce awkward postures in drywall installers. Five coupling tools were evaluated using the Lumbar Motion Monitor that measures trunk kinematics and predicts probability of low back disorder group membership risk (LBD risk). Workers answered surveys about their comfort while using each tool. The results indicate that use of the 2-person manual lift and the J-handle provide the best reduction in awkward postures, motions, low back sagittal moment, and LBD risk. The two-person manual lift appears to be the safest method of lifting and moving drywall, though using the two-person J-handle also significantly reduces injury risk. Given that carpenters are skeptical about using equipment that can get in the way or get lost, a practical recommendation is promotion of two-person manual lifting. For single-person lifts, the Old Man tool is a viable option to decrease risk of MSDs. 相似文献
107.
Box–Jenkins (1970) models are often used to capture the autoregressive moving average of past observations of tourist arrivals from Japan to Taiwan and New Zealand. However, other explanatory variables, such as real income in the origin country, have also affected the demand for international travel. The purpose of this paper is to use the ARMAX model to investigate the dynamic relationship between tourism demand and real income of Japan, and to compare the findings with the single-equation model. Unit root tests and diagnostics are performed before estimating the income elasticity of travel demand by Japan for New Zealand and Taiwan based on seasonally unadjusted quarterly data for 1980(1) to 2004(2). The empirical results of the ARMAX model support the economic theory that the demand for international travel is positively related to income of the origin country. 相似文献
108.
Proteomics has long been thought to hold the promise of producing results of clinical utility which will influence patient treatment and outcomes. A recent Wellcome Trust/EBI meeting and retreat--“Perspectives in Clinical Proteomics”--brought together experts from a broad range of stakeholder groups with an interest in ensuring proteomics achieves this aim. This viewpoint presents views derived from these forums, proposing a pathway for the development of next-generation proteomic analyses in the clinical setting from selection of candidates through to their validation and ultimate demonstration of utility through health technology assessments. Although not meant to be all encompassing, important elements for proteomics researchers to consider are presented. 相似文献
109.
Qiusheng Wu Haibin Su Douglas J. Sherman Hongxing Liu Jennifer M. Wozencraft Bailang Yu 《International journal of remote sensing》2016,37(20):4854-4873
Hurricanes and tropical storms are severe threats to coastal properties, settlements, and infrastructure. Airborne light detection and ranging (lidar) surveys conducted before and after storm events allow detailed analysis of coastal geomorphologic and sediment volumetric changes and have been proved very useful in the study of coastal changes. Traditionally, most studies use the pixel-based differencing method to quantify the spatial extent and magnitude of coastal changes based on sequential lidar surveys. This research presents a graph theory-based approach and associated software tools for representing and quantifying storm-induced damages to buildings, beaches and sand dunes, coastal vegetation canopy, and infrastructure. Generation of elevation difference grids, construction of local contour trees, and derivation of semantic properties are key components of the new algorithm for change object detection and extraction. An ontology and taxonomy are proposed to classify change objects into different types of coastal damages in terms of their semantic properties. This method has been successfully applied to assess damages of Hurricane Ike to the Bolivar Peninsula on the Texas Gulf Coast based on pre- and post-storm airborne lidar data and colour infrared aerial photographs. 相似文献
110.