全文获取类型
收费全文 | 3727篇 |
免费 | 6篇 |
国内免费 | 2篇 |
专业分类
电工技术 | 23篇 |
化学工业 | 289篇 |
金属工艺 | 89篇 |
机械仪表 | 88篇 |
建筑科学 | 19篇 |
矿业工程 | 11篇 |
能源动力 | 22篇 |
轻工业 | 32篇 |
水利工程 | 64篇 |
石油天然气 | 144篇 |
无线电 | 107篇 |
一般工业技术 | 421篇 |
冶金工业 | 2233篇 |
原子能技术 | 102篇 |
自动化技术 | 91篇 |
出版年
2021年 | 21篇 |
2019年 | 22篇 |
2018年 | 37篇 |
2017年 | 37篇 |
2016年 | 42篇 |
2014年 | 29篇 |
2013年 | 70篇 |
2012年 | 52篇 |
2011年 | 44篇 |
2010年 | 32篇 |
2009年 | 42篇 |
2008年 | 59篇 |
2007年 | 53篇 |
2006年 | 32篇 |
2005年 | 29篇 |
2004年 | 24篇 |
2003年 | 38篇 |
2002年 | 30篇 |
2001年 | 25篇 |
2000年 | 33篇 |
1999年 | 65篇 |
1998年 | 637篇 |
1997年 | 429篇 |
1996年 | 265篇 |
1995年 | 165篇 |
1994年 | 140篇 |
1993年 | 147篇 |
1992年 | 31篇 |
1991年 | 44篇 |
1990年 | 37篇 |
1989年 | 38篇 |
1988年 | 54篇 |
1987年 | 48篇 |
1986年 | 53篇 |
1985年 | 32篇 |
1984年 | 18篇 |
1983年 | 19篇 |
1982年 | 30篇 |
1981年 | 40篇 |
1980年 | 55篇 |
1979年 | 23篇 |
1978年 | 48篇 |
1977年 | 75篇 |
1976年 | 158篇 |
1975年 | 30篇 |
1974年 | 26篇 |
1973年 | 23篇 |
1972年 | 20篇 |
1971年 | 24篇 |
1969年 | 22篇 |
排序方式: 共有3735条查询结果,搜索用时 296 毫秒
101.
102.
S. V. Kidalov F. M. Shakhov A. V. Shvidchenko A. N. Smirnov V. V. Sokolov M. A. Yagovkina A. Ya. Vul’ 《Technical Physics Letters》2017,43(1):53-56
For the first time it has been experimentally shown that a powder of detonation nanodiamonds (DND) and a saturated acyclic hydrocarbon, mono- or dibasic alcohol, used as the reaction mixture after treatment at high pressures (5–8 GPa) and high temperatures (1300–1800°C) results in the formation of diamond single crystals up to 15 micron in size. The Raman spectrum indicates that the diamonds have a perfect of crystal structure. It has been suggested that the oriented attachment mechanism is responsible for growth of micrometer-size diamond single crystals out of DND particles with sizes of about 5 nm under these technological conditions. 相似文献
103.
L. V. Lutsev S. M. Suturin A. M. Korovin V. E. Bursian N. S. Sokolov 《Technical Physics Letters》2018,44(7):558-561
Relaxation losses of magnetic excitations in nanoscale films of Y3Fe5O12 (YIG) were studied. The films were obtained by laser molecular-beam epitaxy (LMBE). Ferromagnetic resonance linewidth ΔH was found to increase sharply as the temperature decreased from 300 to 77 K. The observed growth of ΔH is explained by typical relaxation processes caused by the presence of Fe2+ ions. This effect is not observed in thick films of YIG grown by liquid-phase epitaxy and containing Pb4+ ions, and, hence, we have concluded that the presence of acceptor ions in YIG films obtained by LMBE will facilitate decreasing the concentration of Fe2+ ions and, a result, diminishing relaxation losses. 相似文献
104.
After being poisoned by eating the mushroom species Cortinarius speciosissimus, a twin developed interstitial nephritis with acute renal failure. He received a renal transplant from his living twin brother, who was presumed dizygotic on phenotypic grounds. Fifteen years later, the twins were zygosity tested by DNA "fingerprint analysis" and found to be monozygotic, despite important phenotypic discordances. The recipient has discontinued immunosuppression therapy and remains well after 9 months. We suggest that, for medical and other reasons, zygosity should be determined at birth on all like-sexed twins. 相似文献
105.
SS Cohen DJ Mason LS Arsenie SM Sargese D Needham 《Canadian Metallurgical Quarterly》1998,23(6):48, 54, 57-460 passim
Decades of practice and research suggest that nurse practitioners (NPs) provide cost-effective and high-quality care. Managed care's emphasis on prevention and cost savings led some policy makers to view NPs as a way to meet the need for primary care providers. However, access to and utilization of NPs has increasingly been controlled by managed care organizations (MCOs) through their selection of providers for primary care panels. This study employed qualitative methodology to examine NPs' experiences with MCOs. Three focus groups, comprising 27 NPs in New York and Connecticut, revealed NPs' mixed reactions to managed care and a range of sentiments regarding NPs' efforts to be listed as primary care providers. The results reflected NPs' concerns about their perceived "invisibility," as well as their sense of "invincibility" in the ways in which NPs are responding to the barriers posed by MCOs. They identified barriers to, as well as ways to facilitate, being listed by MCOs, and described the importance of NPs working individually and collectively in negotiating with MCOs. 相似文献
106.
Based on increasing evidence that the type I R subunits as well as the type II R subunits localize to specific subcellular sites, we have carried out an extensive characterization of the stable dimerization domain at the N terminus of RIalpha. Deletion mutants as well as alanine scanning mutagenesis were used to delineate critical regions as well as particular amino acids that are required for homodimerization. A set of nested deletion mutants defined a minimum core required for dimerization. Two single site mutations on the C37H template, RIalpha(F47A) and RIalpha(F52A), were sufficient to abolish dimerization. In addition to serving as a dimerization motif, this domain also serves as a docking surface for binding to dual specificity anchoring proteins (D-AKAPs) (Huang, L. J., Durick, K., Weiner, J. A., Chun, J., and Taylor, S. S. (1997) J. Biol. Chem. 272, 8057-8064; Huang, L. J., Durick, K., Weiner, J. A., Chun, J., and Taylor, S. S. (1997) Proc. Natl. Acad. Sci. U. S. A. 94, 11184-11189). A similar strategy was used to map the sequence requirements for anchoring of RIalpha to D-AKAP1. Although dimerization appears to be essential for anchoring to D-AKAP1, anchoring can also be abolished by the following single site mutations: C37H, V20A, and I25A. These sites define "hot spots" for the anchoring surface since each of these dimeric proteins are deficient in binding to D-AKAP1. In contrast to earlier predictions, the alignment of the dimerization/docking domains of RIalpha and RII show striking similarities yet subtle differences not only in their secondary structure (Newlon, M. G., Roy, M., Hausken, Z. E., Scott, J. D., and Jennings. P. A. (1997) J. Biol. Chem. 272, 23637-23644) but also in the distribution of residues important for both docking and dimerization functions. 相似文献
107.
SA Petrill K Saudino SS Cherny RN Emde DW Fulker JK Hewitt R Plomin 《Canadian Metallurgical Quarterly》1998,69(1):68-74
Two definitions of normality ("isolated" or "correlated") are considered. The boundaries of "isolated" normality were determined by a statistical procedure, whereas the "correlated" approach was related to a clinical or predictive definition. In the latter case, the biological variations were considered abnormal if they implied a hazard with some significant future ailment as a risk factor. In this pragmatic approach, the upper limit of normal/abnormal variations is the point beyond which medical strategy is related to the most expected benefit when applied to a definite population or to an individual patient. The capacity of a diagnostic test to discriminate between patients with a defined risk and those without risk depends strictly on the value of the parameter chosen. In medical care for the prevention of vascular complications in diabetic patients or with foetal risks in pregnant women, the limits of the so-called normal range of glycaemia and other parameters should be determined according to the objective of the preventive and/or therapeutic measures to be prescribed. 相似文献
108.
We have studied a laser system with quick electronic tuning of the spectrum shape and continuous distribution. The proposed method is based on separate control of phase and amplitude spatial distributions of resonator transmittance. Evolution of the spectral function of the diffractively coupled dispersive resonators and the model for the formation of the resonator with the spectral function given by its moments are studied theoretically. The synthesis of continuous spectra is investigated experimentally in the laser with a novel control element including a spatial acousto-optic modulator and a tunable lens telescope. 相似文献
109.
DA Stoyanovosky R Goldman SS Jonnalagadda BW Day HG Claycamp VE Kagan 《Canadian Metallurgical Quarterly》1996,330(1):3-11
Rapidly growing knowledge about the nature and behaviour of breast cancer has led to many treatment modalities. Consequently, the possibilities of individualizing the treatment of breast cancer increase. The major tool for the determination of an optimal treatment plan is the estimation of the extent of the disease: in other words, staging. As a consequence, together with the expected result of the treatment, the stage of the disease gives information on the prognosis of the patient. Current staging systems insufficiently describe the clinically important features of breast cancer with respect to management and outcome: local and regional extent, invasiveness, aggressiveness, the state of dissemination, and the effectiveness of different treatment modalities. For staging of the local and regional extent, histology plays a prominent role and should be incorporated in future staging systems. Histological workup therefore needs standardisation. Histological parameters as tumour size, grade, nodal status, and vascular invasion are also the most important prognostic factors. Many so-called biological prognostic factors are related to the invasiveness and aggressiveness (metastatic potential) of the tumour, and therefore to the prognosis of the patient. However, these factors do not necessarily predict the effectiveness of certain systemic treatments. Only if the biological foundation of a prognostic factor is completely clarified can treatment be based on this knowledge, and the factor will become a predictor for the treatment effect. Many "biological" prognostic factors do not fulfil this main criterion and are therefore not useful for clinical decision making. A clinically useful staging system covers three primary aims: (1) to guide locoregional treatment, (2) to prognosticate the chance of survival, and (3) to indicate who needs what kind of adjuvant treatment. For the conception of a new staging system the following steps should be taken: standardization of all aspects of histology, identification of regional nodal involvement, and validation of prognostic factors with respect to their predictive value to treatment outcome. 相似文献
110.
Previously, we identified PG-1000 as part of a disulfide-linked complex of two large proteoglycans (PG-1000 and the beta component) and three smaller proteins purified from the extracellular matrix of elasmobranch electric organ (Iwata and Carlson, 1991, J. Biol. Chem. 266: 323-333). PG-1000 is a chondroitin sulfate/keratan sulfate proteoglycan with a molecular mass of about 1.2 x 16(6) daltons. When visualized in the electron microscope, PG-1000 has the typical "bottle-brush" appearance expected for a proteoglycan with an average total length of about 345 nm and about 20 chains of approximately 110 nm (Carlson and Wight, 1987, J. Cell Biol. 105: 3075-3086). Using immunocytochemical methods, we now demonstrate that PG-1000 is a component of the interstitial extracellular matrix of the electric organ. PG-1000 immunoreactivity is found throughout the interstitial matrix, but it is highly concentrated in that region of the matrix immediately adjacent to the basal lamina, the reticular lamina. The reticular and basal laminae together form the basement membrane. PG-1000 immunoreactivity is especially apparent on basal laminae that surround nerve fibers and nerve terminals. When the disulfide-linked PG-1000 complexes are purified and examined in the electron microscope following rotary shadowing, they appear as bottle-brush structures which are often attached at a central region and radiate like spokes of a wheel. These aggregates contain two to six proteoglycan monomers. We hypothesize that the PG-1000 complexes are disulfide-stabilized parts of an extended network of linked proteoglycans in the reticular lamina. 相似文献