全文获取类型
收费全文 | 14788篇 |
免费 | 1646篇 |
国内免费 | 1161篇 |
专业分类
电工技术 | 551篇 |
技术理论 | 1篇 |
综合类 | 1304篇 |
化学工业 | 2226篇 |
金属工艺 | 425篇 |
机械仪表 | 834篇 |
建筑科学 | 1658篇 |
矿业工程 | 182篇 |
能源动力 | 597篇 |
轻工业 | 840篇 |
水利工程 | 863篇 |
石油天然气 | 362篇 |
武器工业 | 156篇 |
无线电 | 953篇 |
一般工业技术 | 2362篇 |
冶金工业 | 715篇 |
原子能技术 | 270篇 |
自动化技术 | 3296篇 |
出版年
2024年 | 101篇 |
2023年 | 420篇 |
2022年 | 721篇 |
2021年 | 746篇 |
2020年 | 637篇 |
2019年 | 593篇 |
2018年 | 557篇 |
2017年 | 640篇 |
2016年 | 623篇 |
2015年 | 582篇 |
2014年 | 896篇 |
2013年 | 1026篇 |
2012年 | 913篇 |
2011年 | 968篇 |
2010年 | 694篇 |
2009年 | 774篇 |
2008年 | 772篇 |
2007年 | 833篇 |
2006年 | 681篇 |
2005年 | 630篇 |
2004年 | 526篇 |
2003年 | 459篇 |
2002年 | 415篇 |
2001年 | 360篇 |
2000年 | 293篇 |
1999年 | 259篇 |
1998年 | 221篇 |
1997年 | 182篇 |
1996年 | 144篇 |
1995年 | 154篇 |
1994年 | 109篇 |
1993年 | 92篇 |
1992年 | 79篇 |
1991年 | 70篇 |
1990年 | 76篇 |
1989年 | 71篇 |
1988年 | 62篇 |
1987年 | 34篇 |
1986年 | 17篇 |
1985年 | 23篇 |
1984年 | 17篇 |
1983年 | 26篇 |
1982年 | 15篇 |
1980年 | 9篇 |
1979年 | 8篇 |
1966年 | 6篇 |
1964年 | 6篇 |
1959年 | 7篇 |
1958年 | 5篇 |
1955年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
61.
通过理论推导证明:在外扩散与化学抑制共存的非均相固定化酶促反应中,总有效系数η为外扩散有效系数ηdif和化学抑制有效系数ηch的乘积,并且分别小于相应的ηdif和ηch;从数学上解释了外扩散抑制和一般性化学抑制间所存在的“抗激发互交作用”。利用所得公式计算表明:底物浓度对外扩散与竞争性、非竞争性和反竞争性等不同化学抑制共存的非均相固定化酶促反应有明显不同的影响;扩散抑制均显著地影响非均相固定化酶促反应,使得反应体系的总有效系数随抑制作用的增加而明显减小,从而对这类反应有了更进一步的认识 相似文献
62.
The solubility parameter of poly(ethylene oxide) at 25°C has been determined using the method developed by DiPaola-Baranyi and Guillet, by the extrapolation of the values of the interaction parameter χ, at high temperatures, ranging from 70°–90°, 90°–110° and 110°–130°C down to 25°C. The values of the solubility parameter obtained, depending on the temperature ranges employed, are 9.8, 9.9 and 10.1, respectively. 相似文献
63.
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
64.
Slow growth and high seedling mortality limit direct seeding establishment of guayule (Parthenium argentatum G.). This study was conducted to assess seedling growth enhancement by the addition of different rates and forms of N fertilizers and Ca salts. Experiments were conducted in a greenhouse with cultivar 593 under both surface and subirrigated conditions using water low in salts (salinity of 0.8 dSm–1, SAR of 5.0 and 10 mg Ca L–1). Under surface-irrigated conditions, seedling height and fresh plant weight increased with N application to the irrigation water to 70 mg L–1. The best seedling growth was observed when (NH4)2SO4 was added in combination with CaCl2 or CaSO4. Progressively less growth was observed by addition of (NH4)2SO4 alone, CO(NH2)2 plus CaSO4, CO(NH2)2 alone and Ca(NO3)2. When seedlings were subirrigated, however, the best growth was observed with Ca(NO3)2. Intermediate growth was obtained with (NH4)2SO4 plus CaSO4 and lowest growth rates with (NH4)2SO4 alone. These differential responses may be explained by the differences in leaching and volatile characteristics of the N forms. Growth enhancement from N and Ca additions increased with time with significant increases 45 days after seeding. Nitrogen application with Ca may be effective amendment in promoting subsequent growth of direct seeded guayule. 相似文献
65.
M. Takeuchi S. Ueno E. Flöter K. Sato 《Journal of the American Oil Chemists' Society》2002,79(7):627-632
The binary phase behavior of SOS (1,3-distearoyl-2-oleoyl-sn-glycerol) and SLS (1,3-distearoyl-2-linoleoyl-sn-glycerol) was examined by using DSC and conventional and synchrotron radiation X-ray diffraction. The solid-solution phases
were observed in the metastable α and γ forms in all concentration ranges. Results indicated that the miscible γ form did
not transform to the β′ form when the mixtures were subjected to simple cooling from a high-temperature liquid to a low-temperature
solid phase. However, and α-melt-mediated transformation into β′ and β2 resulted in the formation of immiscible phases in concentration ranges of SLS below 30%. By contrast, at SLS concentration
ranges above 30%, the α-melt-mediated transformation caused crystallization of only the γ form, and β′ and β2 crystals did not appear. These results show that the specific interactions between SOS and SLS are operative in the phase
behavior of the mixture states of SOS and SLS. 相似文献
66.
Computing scattering rates of electrons and phonons stands at the core of studies of electron transport properties. In the high field regime, the interactions between all electron bands with all phonon bands need to be considered. This full band interaction implies a huge computational burden in calculating scattering rates. In this study, a new accelerated algorithm is presented for this task, which speeds up the computation by two orders of magnitude (100 times) and dramatically simplifies the coding. At the same time, it visually demonstrates the physical process of scattering more clearly. 相似文献
67.
We present implementations of the numerical integration of systems with long-range interactions on graphic processing units for three N-body models with long-range interactions of general interest: the Hamiltonian Mean Field, Ring and two-dimensional self-gravitating models. We discuss the algorithms, speedups and errors using one and two GPU units. Speedups can be as high as 140 compared to a serial code, and the overall relative error in the total energy is of the same order of magnitude as for the CPU code. The number of particles used in the tests range from 10,000 to 50,000,000 depending on the model. 相似文献
68.
The effectiveness of an active shutter-glasses stereoscopic display (SD) and a passive polarised SD was evaluated in a live robot-teleoperation task and a simulated indirect-vision driving task in various terrains. Overall, participants completed their tasks significantly faster with the SDs in three-dimensional (3D) mode than with the SDs in the baseline 2D mode. They also navigated more accurately with the SDs in 3D mode. When the effectiveness of the two types of SDs was examined separately, results showed that the active shutter-glasses SD resulted in faster responses and task completion times than the passive polarised SD, though most of the differences failed to reach statistical significance. Perceived workload when interacting with the two SD systems did not differ significantly between the active versus passive display types or between the 3D and 2D modes of operation; however, participants reported more severe discomfort after interacting with the passive polarised SD. 相似文献
69.
The behavioral and physiological effects of plant allelochemicals have been difficult to demonstrate; it is not often clear whether the compounds are deterrent, toxic, or both. In this study, we compared the qualitative and quantitative effects of several iridoid glycosides on a generalist lepidopteran herbivore,Spodoptera eridania (Noctuidae). Larval growth and survivorship and larval preference or avoidance were measured on artificial diets containing different iridoid glycosides at different concentrations. We also tested the toxicity/deterrence of these compounds. We found that iridoid glycosides retarded larval growth significantly at relatively low concentrations and that they were usually avoided in preference tests. The toxicity/ deterrence test did not always reflect the results of these other tests. The merits of using a variety of methods for determining deterrence and/or toxicity of plant allelochemicals are discussed. 相似文献
70.
L. B. Brattsten 《Journal of chemical ecology》1988,14(10):1919-1939
Herbivorous insects have the capacity to develop behavioral, physiological, and biochemical resistance mechanisms in response to chemical selection pressures. Among natural insect-plant associations, there are several cases of target-site insensitivity to and enhanced metabolism of plant allelochemicals. There are also known instances of physiological defenses such as extra rapid excretion or storage of toxic compounds. Multiple defenses seem to be prevalent in natural insect-plant interactions that involve toxic compounds, possibly reflecting the long time these interactions have had to evolve compared to insect-synthetic insecticide interactions. Synthetic insecticides were introduced about 45 years ago. Until recently they have been used as single-active-component preparations. As such, they have been and are very effective in producing insect populations with enhanced detoxification ability and target-site insensitivity. Most insecticide-resistant insect populations have one major defense mechanism. This feature makes the synthetic insecticides very useful tools for studies of insect defenses against toxic chemicals. Information gained from studies with insecticides can shed light on the capabilities of insects to adapt to toxicants in their environment. In assessing the validity of work with synthetic insecticides for natural systems, the fundamental differences between these substances and allelochemicals, and in their presentation to the insects, must, however, be considered. The prevalence of multiple defenses and reliance on modified physiological processes in natural interactions may reflect different properties of the natural chemicals in being generally highly biodegradable and often less acutely toxic than synthetic insecticides. In many cases, the plant allelochemicals are presented to the insects as mixtures. It is, however, to be expected that pest insects will evolve effective multiple defenses against synthetic insecticides. About 20% of all resistant populations have already developed multiple defenses, in most cases combinations of enhanced metabolism and target-site insensitivity. This implies that current crop protection practices need to be modified to ensure the continued usefulness of synthetic insecticides. To achieve this, it is important to study intensively not only insect-insecticide interactions but also the interactions operating in natural insect-plant associations. 相似文献