首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   173701篇
  免费   1436篇
  国内免费   242篇
电工技术   2622篇
综合类   131篇
化学工业   27699篇
金属工艺   9578篇
机械仪表   5874篇
建筑科学   3125篇
矿业工程   1915篇
能源动力   2983篇
轻工业   9249篇
水利工程   2783篇
石油天然气   8731篇
武器工业   12篇
无线电   15075篇
一般工业技术   39409篇
冶金工业   28294篇
原子能技术   6987篇
自动化技术   10912篇
  2021年   1972篇
  2019年   1863篇
  2018年   3276篇
  2017年   3347篇
  2016年   3595篇
  2015年   1837篇
  2014年   3163篇
  2013年   6747篇
  2012年   4549篇
  2011年   5661篇
  2010年   4590篇
  2009年   5042篇
  2008年   5076篇
  2007年   4994篇
  2006年   4250篇
  2005年   3890篇
  2004年   3689篇
  2003年   3592篇
  2002年   3501篇
  2001年   3504篇
  2000年   3402篇
  1999年   3262篇
  1998年   7157篇
  1997年   5268篇
  1996年   3907篇
  1995年   2979篇
  1994年   2648篇
  1993年   2771篇
  1992年   2288篇
  1991年   2346篇
  1990年   2441篇
  1989年   2343篇
  1988年   2336篇
  1987年   2215篇
  1986年   2277篇
  1985年   2320篇
  1984年   2231篇
  1983年   2160篇
  1982年   1992篇
  1981年   2206篇
  1980年   2064篇
  1979年   2276篇
  1978年   2446篇
  1977年   2446篇
  1976年   3111篇
  1975年   2247篇
  1974年   2311篇
  1973年   2350篇
  1972年   2161篇
  1971年   1915篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
981.
From November 1992 to February 1993, 455 red deer (Cervus elaphus) were surveyed in order to estimate the prevalence of warble fly (Hypoderma actaeon) larvae under the skin of this ungulate species. Material came from Montes de Toledo, Sierra Morena, Sierra de Alcaraz, and Sierras de Cazorla, Segura y Las Villas Natural Park (central and southern Spain). We observed a prevalence of 92%, with a mean +/- SD intensity of 35.7 +/- 41.3 grubs per parasitized host; there was a maximum of 317 larvae per host. No significant differences in prevalence by host sex were found, although significant differences were observed in prevalences among different host age classes. The main location of feeding larvae in deer was in the back tissues.  相似文献   
982.
A statistically admissible solution has been constructed for a pipe with an axial through crack. The boundaries of the limit region have been obtained and the strength conditions on its boundary have been formulated. The extension of the distribution of forces and moments beyond the limit region boundary has been substantiated. The results obtained for a pipe with closed ends are in fair agreement with the experimental data. The influence of the axial force and the property anisotropy upon the fracture stress has been studied. The possibility of considering several cracks is analysed.  相似文献   
983.
The authors show the decisive role and special features of heat and mass transfer in the mechanism of abnormal plasticity and in formation of thermomechanical dissipative structures under large plastic strains by the examples of computer modeling of stretching of a specimen, high-pressure torsional shear in a Bridgeman chamber, and shearing strain of a material in the form of flow of a quasiviscous liquid in a channel with local heat removal via a stationary wall.Izhevsk Mechanical Institute. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 67, Nos. 1–2, pp. 127–131, July–August, 1994.  相似文献   
984.
The residential therapeutic caring community (RTCC) for adolescents combines psychotherapeutic principles of the professional model and self-help concept of the therapeutic community by using the collective resources of members to mobilize peer pressure. The RTCC is a safe, structured, supportive treatment environment that employs a confrontation, teaching, interpretative, and reasoning approach and uses the psychotherapeutic principles of reality therapy and existential thought. In the RTCC, the staff serve as mentors and role models, and they demonstrate their concern by maintaining high expectations for immediate improved behavior. The personal qualities necessary for a psychotherapist working in an RTCC are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
985.
This paradigm distinguished between two hypotheses not previously directly addressed. Do repeated exposures to cocaine at critical times during pregnancy, when the neural mechanisms that support maternal behavior are being readied, alter some fundamental neural underpinning of maternal behavior in rats? Alternatively, does cocaine alter maternal behavior only when circulating? During the 4 hr after cocaine injection (20 or 40 mg/kg), there were significant deficits in maternal behavior. In contrast, 16 hr after cocaine injection, drug-injected females, in which plasma cocaine had fallen to nondetectable levels, showed the normal maternal behavior of saline-injected controls. This pattern of impaired maternal behavior after cocaine injection, followed by normal behavior as blood levels returned to zero, was replicated over 8 days. It was concluded that cocaine impairs maternal behavior only when circulating and does not have a residual effect in the transiently drug-free, chronically drug-treated dam. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
986.
The Roussy-Lévy syndrome (MIM #180800) was described in 1926 as a disorder presenting with pes cavus and tendon areflexia, distal limb weakness, tremor in the upper limbs, gait ataxia and distal sensory loss. We report a family with affected members in four generations, showing these clinical signs of Roussy-Lévy syndrome and a partial duplication at chromosome 17p11.2. This genetic defect is commonly found in patients with the hypertrophic form of the Charcot-Marie-Tooth syndrome. Our finding provides evidence against the Roussy-Lévy syndrome as a distinct entity but suggests a close relation with the Charcot-Marie-Tooth syndrome. What causes the additional features of gait ataxia and essential tremor needs further clarification.  相似文献   
987.
Plasmodium falciparum secretes several proteins that cause changes in the erythrocyte membrane enabling it to survive within red blood cells. Little is known of the mechanisms involved in the secretion and targeting of parasite polypeptides to the various cell compartments. The P. falciparum gene homologous to the mammalian Sec61alpha, gene, which encodes a component of the translocation pore in the endoplasmic reticulum of eukaryotic cells, was characterised to investigate the translocation process in the parasite. PfSec61 is present as a unique copy in the parasite genome and was mapped to chromosome 13. It encodes a 40 kDa polypeptide, as shown by immunoblotting and immunoprecipitation of [35S]methionine metabolically-labelled parasite extracts. The deduced amino acid sequence of PfSec61 is 87% similar to the mammalian polypeptide, and the two proteins give similar hydropathy plots. These results strongly suggest that PfSec61 has the same topological orientation and functional role as Sec61alpha. Anti-PfSec61 antibodies were used to investigate the cellular location and kinetics of expression of the polypeptide in the parasite. Immunofluorescence confocal microscopy showed that PfSec61 was located in the parasite cytoplasm, close to the nucleus, in a position consistent with its being in the endoplasmic reticulum.  相似文献   
988.
989.
A way to increase the chemical resistance of glass containers by injecting a quantity (0.2–1.0 ml) of a special reagent solution into freshly shaped items is considered.Translated from Steklo i Keramika, No. 5, pp. 8–11, 1996.  相似文献   
990.
Eighty-four patients with locally advanced, non metastatic squamous cell carcinoma of head and neck or esophagus, were included in a multicentric double-blind randomized trial, comparing goralatide (12.5 or 62.5 micrograms/kg/day, d1-d4) to placebo, associated with carboplatin (400 mg/m2, d1) and 5-fluorouracile (1 g/m2/d continuous IV over 96 hours). Haematological toxicity was analysed on 221 cycles of chemotherapy. All but one patient were evaluable because of early death without haematological toxicity. No significant difference was observed for mean nadir of leukocytes, granulocytes, platelets counts and hemoglobin level. Duration of haematological toxicity was no significantly different for the two groups of patients. Anemia and lymphopenia were more frequent in the goralatide treated patients. Clinical and biological tolerability of goralatide was excellent.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号