全文获取类型
收费全文 | 9308篇 |
免费 | 142篇 |
国内免费 | 10篇 |
专业分类
电工技术 | 90篇 |
综合类 | 5篇 |
化学工业 | 1232篇 |
金属工艺 | 162篇 |
机械仪表 | 227篇 |
建筑科学 | 280篇 |
矿业工程 | 55篇 |
能源动力 | 164篇 |
轻工业 | 696篇 |
水利工程 | 70篇 |
石油天然气 | 19篇 |
武器工业 | 1篇 |
无线电 | 748篇 |
一般工业技术 | 1339篇 |
冶金工业 | 3520篇 |
原子能技术 | 81篇 |
自动化技术 | 771篇 |
出版年
2022年 | 48篇 |
2021年 | 54篇 |
2020年 | 40篇 |
2019年 | 55篇 |
2018年 | 78篇 |
2017年 | 73篇 |
2016年 | 84篇 |
2015年 | 80篇 |
2014年 | 99篇 |
2013年 | 354篇 |
2012年 | 194篇 |
2011年 | 252篇 |
2010年 | 252篇 |
2009年 | 236篇 |
2008年 | 254篇 |
2007年 | 252篇 |
2006年 | 216篇 |
2005年 | 238篇 |
2004年 | 175篇 |
2003年 | 196篇 |
2002年 | 189篇 |
2001年 | 158篇 |
2000年 | 173篇 |
1999年 | 178篇 |
1998年 | 931篇 |
1997年 | 662篇 |
1996年 | 466篇 |
1995年 | 340篇 |
1994年 | 294篇 |
1993年 | 308篇 |
1992年 | 118篇 |
1991年 | 119篇 |
1990年 | 130篇 |
1989年 | 139篇 |
1988年 | 141篇 |
1987年 | 107篇 |
1986年 | 95篇 |
1985年 | 122篇 |
1984年 | 115篇 |
1983年 | 86篇 |
1982年 | 77篇 |
1981年 | 81篇 |
1980年 | 91篇 |
1979年 | 80篇 |
1978年 | 93篇 |
1977年 | 151篇 |
1976年 | 269篇 |
1975年 | 63篇 |
1974年 | 63篇 |
1973年 | 57篇 |
排序方式: 共有9460条查询结果,搜索用时 7 毫秒
71.
MN Janakiraman KD Watenpaugh PK Tomich KT Chong SR Turner RA Tommasi S Thaisrivongs JW Strohbach 《Canadian Metallurgical Quarterly》1998,8(10):1237-1242
Potent, non-peptidic, dihydropyrone sulfonamide HIV protease inhibitors have been previously described. Crystallographic analysis of dihydropyrone sulfonamide inhibitor/HIV protease complexes suggested incorporation of a second, C2 symmetry-related sulfonamide group. Selected bis-sulfonamide dihydropyrone analogues display high HIV protease inhibitory activity. 相似文献
72.
DM Foreman S Jones NM McKechnie G Williams ME Boulton 《Canadian Metallurgical Quarterly》1996,28(5):296-302
We describe a simple method for combining in situ hybridisation and immunohistochemistry on the same retinal section. The technique was developed using a radiolabelled cDNA probe for opsin and an antibody (ROS1F4) against rhodopsin. This method retains the antigenic sites if immunocytochemistry is performed prior to in situ hybridisation. Opsin mRNA was found in the photoreceptor inner segment with rhodopsin immunolocalised to the photoreceptor outer segments. The technique should be applicable to numerous situations including analysis of the sequence of events in the expression and synthesis of the various opsins during retinal development and degeneration. 相似文献
73.
The multicopy c subunit of the H+-transporting ATP synthase of Escherichia coli folds through the transmembrane F0 sector as a hairpin of two hydrophobic alpha-helices with the proton-translocating aspartyl-61 side chain centered in the second transmembrane helix. The number of subunits c in the F0 complex, which is thought to determine the H+-pumping/ATP stoichiometry, was previously not determined with exactness but thought to range from 9-12. The studies described here indicate that the exact number is 12. Based upon the precedent of the subunit c in vacuolar-type ATPases, which are composed of four transmembrane helices and seem to have evolved by gene duplication of an F0-type progenitor gene, we constructed genetically fused dimers and trimers of E. coli subunit c. Both the dimeric and trimeric forms proved to be functional. These results indicate that the total number of subunit c in F0 should be a multiple of 2 and 3. Based upon a previous study in which the oligomeric organization of c subunits in F0 was determined by cross-linking of Cys-substituted subunits (Jones, P. C. , Jiang, W., and Fillingame, R. H. (1998) J. Biol. Chem. 273, 17178-17185), we introduced Cys into the first and last transmembrane helices of subunit c monomers, dimers, and trimers and attempted to generate cross-linked products by oxidation with Cu(II)-(1,10-phenanthroline)2. Double Cys substitutions at two sets of positions gave rise to extensive cross-linked multimers. Multimers of the monomer that extended up to the position of c12 were correlated and calibrated with distinct cross-linked species of the appropriate doubly Cys-substituted dimers (i.e. c2, c4, . c12) and doubly Cys-substituted trimers (i.e. c3, c6, c9, c12). The results show that there are 12 copies of subunit c per F0 in E. coli, the exact number having both mechanistic and structural significance. 相似文献
74.
75.
RM Summers J Andrasko-Bourgeois IM Feuerstein SC Hill EC Jones MK Busse B Wise KE Bove BA Rishforth E Tucker TL Spray JM Hoeg 《Canadian Metallurgical Quarterly》1998,98(6):509-518
Hepatitis C chronically infects approximately 1.5% of Americans and is the most common clinical problem facing hepatologists. Since the virus was initially described in 1989, development of an effective therapy has been challenging. Although several different therapeutic agents have been used, no therapy has been shown to reliably eradicate the virus. Interferon-alpha, a cytokine with immunostimulatory and anti-viral properties, has become the therapy of choice for patients with chronic hepatitis C infection. Trials assessing the efficacy of interferon-alpha have characterized host and viral factors predictive of responses to treatment. A thorough understanding of these predictive factors is requisite to providing cost-effective therapeutic decisions for the patient with chronic hepatitis C infection. 相似文献
76.
The lens epithelium of the human eye plays a crucial role in the pathogenesis of primary and secondary cataract. Sixty hematoxylin-eosinstained lens epithelia were examined using a light microscope. Cell parameters were compared to one another in the various age groups of patients, between patients with secondary cataract (radiation cataract, steroid cataract and traumatic cataract) and patients with senile cataract, and between male and female patients. The t-test was used for statistical comparison. The median cell density was 3116.5 cells/mm2. The median nucleus-plasma ratio was 1:2.74. Patients with secondary cataract had a larger medium cell and nucleus area as well as a higher nucleus-plasma ratio and a lower cell density than patients with senile cataract. A part from degenerative and proliferative cell changes we found various cell types. The age of patients and the cause of cataract correlate with morphometric changes of lens epithelium cells. However, there was no correlation between specific cytologic changes and causes of cataract. 相似文献
77.
Activation of auditory cortex during silent lipreading 总被引:1,自引:0,他引:1
GA Calvert ET Bullmore MJ Brammer R Campbell SC Williams PK McGuire PW Woodruff SD Iversen AS David 《Canadian Metallurgical Quarterly》1997,276(5312):593-596
Watching a speaker's lips during face-to-face conversation (lipreading) markedly improves speech perception, particularly in noisy conditions. With functional magnetic resonance imaging it was found that these linguistic visual cues are sufficient to activate auditory cortex in normal hearing individuals in the absence of auditory speech sounds. Two further experiments suggest that these auditory cortical areas are not engaged when an individual is viewing nonlinguistic facial movements but appear to be activated by silent meaningless speechlike movements (pseudospeech). This supports psycholinguistic evidence that seen speech influences the perception of heard speech at a prelexical stage. 相似文献
78.
A Mitchener DJ Wyper J Patterson DM Hadley JT Wilson LC Scott M Jones GM Teasdale 《Canadian Metallurgical Quarterly》1997,62(6):633-636
We report a case of cervicofacial necrotizing fasciitis that developed after blepharoplasty, an occurrence that, to our knowledge, has not previously been reported in the medical literature. A patient who presented to our institution 3 days after undergoing blepharoplasty of the upper eyelid was diagnosed as having fulminant fasciitis involving extensive areas of the face, scalp, and neck. We review the case in detail and discuss clinical and radiological clues to diagnosis, surgical and medical management, wound care, and subsequent scar contracture. This case emphasizes the need for individualized, appropriate postoperative care and for an awareness of this rare, potentially fatal complication. Early recognition and aggressive treatment of cervicofacial fasciitis can arrest its rapid progression and prevent devastating sequelae. 相似文献
79.
S Jones 《Canadian Metallurgical Quarterly》1997,12(12):28-31
A new method of impulse magnetic therapy was studied in the treatment of neurologic complications of osteochondrosis and deforming spondylarthrosis in 225 patients with neurologic manifestations of pathology in cervical or sacral parts of spinal column. To assess the results obtained, EMG, thermography and determination of the levels of blood plasma lipid peroxidation were used. 相似文献
80.
Fatigue properties of cast aluminum components are controlled by maximum defect size in the material. The larger the maximum
defect size, the lower the fatigue strength and life. In the presence of casting defects, crack initiation can be ignored
and fatigue life is mainly spent in crack propagation. Therefore, fatigue life of aluminum castings can be predicted by long
or short crack growth models. The main problem is defining a starting defect size from readily available data, such as twodimensional
(2-D) pore size measurements on metallographic sections. In this article, an extremevalue statistics (EVS) method was used
to estimate the maximum defect size in 319 castings from conventional metallographic data. The maximum defect size predicted
by EVS agrees quite well with the initiation defect sizes measured from fracture surfaces, and the predicted fatigue life
is in reasonable agreement with the experimental data. 相似文献