全文获取类型
收费全文 | 5263篇 |
免费 | 182篇 |
国内免费 | 4篇 |
专业分类
电工技术 | 59篇 |
综合类 | 6篇 |
化学工业 | 867篇 |
金属工艺 | 95篇 |
机械仪表 | 156篇 |
建筑科学 | 211篇 |
矿业工程 | 38篇 |
能源动力 | 120篇 |
轻工业 | 571篇 |
水利工程 | 36篇 |
石油天然气 | 14篇 |
无线电 | 410篇 |
一般工业技术 | 694篇 |
冶金工业 | 1383篇 |
原子能技术 | 30篇 |
自动化技术 | 759篇 |
出版年
2023年 | 27篇 |
2022年 | 54篇 |
2021年 | 86篇 |
2020年 | 66篇 |
2019年 | 83篇 |
2018年 | 100篇 |
2017年 | 87篇 |
2016年 | 114篇 |
2015年 | 90篇 |
2014年 | 111篇 |
2013年 | 301篇 |
2012年 | 165篇 |
2011年 | 238篇 |
2010年 | 168篇 |
2009年 | 180篇 |
2008年 | 204篇 |
2007年 | 193篇 |
2006年 | 182篇 |
2005年 | 152篇 |
2004年 | 133篇 |
2003年 | 119篇 |
2002年 | 135篇 |
2001年 | 80篇 |
2000年 | 93篇 |
1999年 | 111篇 |
1998年 | 349篇 |
1997年 | 220篇 |
1996年 | 169篇 |
1995年 | 106篇 |
1994年 | 98篇 |
1993年 | 113篇 |
1992年 | 56篇 |
1991年 | 45篇 |
1990年 | 42篇 |
1989年 | 54篇 |
1988年 | 42篇 |
1987年 | 41篇 |
1986年 | 45篇 |
1985年 | 58篇 |
1984年 | 42篇 |
1983年 | 53篇 |
1982年 | 58篇 |
1981年 | 50篇 |
1980年 | 55篇 |
1979年 | 43篇 |
1978年 | 37篇 |
1977年 | 34篇 |
1976年 | 65篇 |
1975年 | 38篇 |
1973年 | 22篇 |
排序方式: 共有5449条查询结果,搜索用时 15 毫秒
61.
We report the use of magnetic resonance imaging (MRI) for in situ tumor growth rate studies of experimental intracranial 9L tumors. T2-weighted spin-echo coronal magnetic resonance images of rat brains with 9L tumors were obtained every 2 days beginning at 8-11 days postimplantation using a 7 tesla MRI system. Tumors were clearly delineated in the images as a hyperintense region with a relatively well-demarcated border and minimal peritumoral edema. Tumor volumes from individual slices were summed together to yield the total tumor volume. The accuracy of this methodology for volumetric determination was verified by MRI phantom studies. Tumor growth rates determined from sequential MRI measurements of tumor volumes were quantitated in terms of volumetric doubling time. Tumor doubling times were found to range from 50 to 81 h, with an average of 66 +/- 8 h (n = 10). Intracranial 9L tumors were found to grow exponentially over the entire life span of the animal, allowing treated animals to serve as their own controls since the volumetric doubling time could be determined from three to four MRI scans before treatment administration. The intracerebral tumor growth delay following a single injection of 1, 3-bis(2-chloroethyl)-1-nitrosourea (13.3 mg/kg i.p.) allowed for noninvasive determination of in vivo log cell kill. A 2.0 +/- 0.2 (n = 3) log cell kill from 1,3-bis(2-chloroethyl)-1-nitrosourea treatment was found from post-treatment MRI volume measurements. These results demonstrate that MRI provides a powerful and sensitive method for assessing the growth and treatment response of intracranial 9L tumors in the rat. 相似文献
62.
L. M. da Cruz Simões 《Structural and Multidisciplinary Optimization》1992,5(1-2):76-83
Virtually all structural optimization based on system reliability was conducted considering continuous design variables. The solution of the reliability-based design problem is obtained by solving alternatively a reliability assessment problem and an optimal sizing program until the best reliability-based design occurs. The reliability assessment problem is formulated as a linearly constrained concave quadratic program. By introducing the concept of segmental members, the discrete optimum design is achieved based upon linear programming. Examples are solved by employing the proposed computational technique.Presented at NATO ASI Optimization of Large Structural Systems, Berchtesgaden, Germany, Sept. 23 – Oct. 4, 1991 相似文献
63.
64.
Refractive index increments and density increments have been measured at 307.6K for polystyrene in binary solvents of 1,2,3,4-tetrahydronaphthalene (tetralin, TET) and cyclohexane over the whole range of solvent composition. Comparison of these increments with the corresponding values obtained at dialysis equilibrium (i.e. at constant chemical potential of low molecular weight species) yielded the coefficients of selective adsorption (γ1) of TET by the polymer. Positive values of γ1 were exhibited at solvent compositions up to 78% (v/v) of the thermodynamically better solvent, TET. Theoretical curves of γ1 vs. composition were calculated on the basis of, firstly, relevant interaction parameters and, secondly, interaction parameters in conjunction with solubility parameters. Both procedures afforded self-consistent results, which were, however, uniformly lower than the experimental values of γ1. 相似文献
65.
Previously obtained cloud point curves for mixtures of oligomeric poly(dimethyl siloxanes) (weight fraction W1) with oligomeric polyethylenes have been supplemented by the use of samples of higher molecular weight. Initial flat regions at low-medium W1 as well as a slight shoulder at extremely high W1 are now considered to be due to crystallization, since the temperatures at which they occur are the melting points of the oligoethylenes. The actual cloud point curves were of an unsymmetrical dome shape, the form of which could not be simulated by using a concentration-independent interaction parameter g in the Flory-Huggins equation. However, spinodals calculated by assuming a quadratic dependence of g on composition were of the same shape as the experimental cloud point curves. The critical compositions calculated on this basis were also close to the experimental ones. 相似文献
66.
A new type of ion implantation technique is used to create a non-equilibrium Pt-Sn(IMP) near-surface alloy with ca. 8.6 at%
Sn. The surface composition was determined by low-energy ion-scattering (LEIS). The kinetics of the electrooxidation of CO
and 2% CO/H2 mixtures on Pt-Sn(IMP) is essentially identical to that of Pt3Sn(110). The fact that any non-equilibrium composition can be easily prepared by this implantation method opens an interesting
practical opportunity to create a new Pt-Sn alloy fuel cell catalyst having an otherwise unobtainable surface composition
of Sn. This method also appears to have general utility in alloy catalysis as a means of exploring compositions in thermodynamically
unfavorable regions of the bulk phase diagram.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
67.
Identical twins pose a great challenge to face recognition due to high similarities in their appearances. Motivated by the psychological findings that facial motion contains identity signatures and the observation that twins may look alike but behave differently, we develop a talking profile to use the identity signatures in the facial motion to distinguish between identical twins. The talking profile for a subject is defined as a collection of multiple types of usual face motions from the video. Given two talking profiles, we compute the similarities of the same type of face motion in both profiles and then perform the classification based on those similarities. To compute the similarity of each type of face motion, we give higher weights to more abnormal motions which are assumed to carry more identity signature information. 相似文献
68.
The synthesis of a series of dyes derived from reaction of 2-methyl-4-(N-ethyl-N-hydroxyethyl)amino, lidicyano-styrene with acid chlorides, chloroformates, isocyanates and isothiocyanates is described. Data relevant to dye characterization by electron-impact induced fragmentation is reported. Dyeing and fastness properties of the dyes on cellulose secondary acetate, cellulose triacetate, nylon 6.6 and polyester fibres are discussed in terms of dye structure. Comparison is made between some related dyes derived from 2-methyl-4-(N-ethyl-N-β-aminoethyljamino-β,βdicyanostyrene. 相似文献
69.
Bargaining is an effective paradigm to solve the problem of resource allocation. The consideration of factors such as bounded rationality of negotiators, time constraints, incomplete information, and complexity of dynamic environment make the design of optimal strategy for one-shot bargaining much tougher than the situation that all bargainers are assumed to be absolutely rational. Lots of prediction-based strategies have been explored either based on assuming a finite number of models for opponents, or focusing on the prediction of opponent’s reserve price, deadline, or the probabilities of different behaviors. Following the methods of estimating opponent’s private information, this paper gives a strategy which improves the BLGAN strategy to adapt to various possible bargaining situations and deal with multifarious opponents. In addition, this paper compares the improved BLGAN strategy with related work. Experimental results show that the improved BLGAN strategy can outperform related ones when faced with various opponents, especially the agents who frequently change their strategies for anti-learning. 相似文献
70.
The honey bee,Apis mellifera, is one of only a few species of phytophagous insects known to be unable to convert C-24 alkyl phytosterols to cholesterol.
Regardless of the dietary sterols available to worker bees, the major tissue sterol of brood reared by the workers is always
24-methylenecholesterol, followed by sitosterol and isofucosterol. Normally, little or no cholesterol is present in honey
bee sterols. The maintenance of high levels of certain sterols is accomplished through a selective transfer of sterols from
the endogenous sterol pools of the workers to the developing larvae through the brood food material secreted from the hypopharyngeal
and mandibular glands and/or the honey stomach of the workers. The selective uptake and transfer of radiolabeled C27, C28 and C29 sterols have been studied to correlate these aspects of sterol utilization with the discovery of an unusual molting hormone
(ecdysteroid) in honey bee pupae as the major ecdysteroid of this stage of development. The phylogenetic implications of this
selective transfer phenomenon in the honey bee and comparison with sterol metabolism in certain other hymenopteran species
emphasize the diversity of steroid biochemistry in insects. 相似文献