全文获取类型
收费全文 | 1763篇 |
免费 | 3篇 |
专业分类
化学工业 | 15篇 |
金属工艺 | 6篇 |
机械仪表 | 3篇 |
建筑科学 | 1篇 |
能源动力 | 1篇 |
轻工业 | 11篇 |
水利工程 | 1篇 |
无线电 | 9篇 |
一般工业技术 | 8篇 |
冶金工业 | 1696篇 |
原子能技术 | 2篇 |
自动化技术 | 13篇 |
出版年
2023年 | 1篇 |
2020年 | 1篇 |
2019年 | 2篇 |
2018年 | 4篇 |
2017年 | 1篇 |
2015年 | 2篇 |
2014年 | 2篇 |
2013年 | 6篇 |
2012年 | 2篇 |
2009年 | 2篇 |
2008年 | 2篇 |
2007年 | 3篇 |
2006年 | 1篇 |
2005年 | 3篇 |
2004年 | 1篇 |
2003年 | 6篇 |
2002年 | 3篇 |
1999年 | 46篇 |
1998年 | 501篇 |
1997年 | 305篇 |
1996年 | 209篇 |
1995年 | 95篇 |
1994年 | 96篇 |
1993年 | 111篇 |
1992年 | 15篇 |
1991年 | 33篇 |
1990年 | 24篇 |
1989年 | 23篇 |
1988年 | 23篇 |
1987年 | 14篇 |
1986年 | 12篇 |
1985年 | 15篇 |
1983年 | 3篇 |
1982年 | 8篇 |
1981年 | 13篇 |
1980年 | 16篇 |
1979年 | 3篇 |
1978年 | 2篇 |
1977年 | 46篇 |
1976年 | 102篇 |
1975年 | 1篇 |
1968年 | 1篇 |
1966年 | 1篇 |
1965年 | 1篇 |
1961年 | 1篇 |
1956年 | 1篇 |
1955年 | 3篇 |
排序方式: 共有1766条查询结果,搜索用时 20 毫秒
1.
PURPOSE: We investigated Sertoli cells in testicular biopsies with carcinoma in situ (CIS) in respect to cytokeratin expression to elucidate the status of Sertoli cell differentiation adjacent to CIS in human testes. Cytokeratin 18 intermediate filaments indicate a state of undifferentiation usually observed in Sertoli cells of prepubertal testes. MATERIALS AND METHODS: 29 testicular biopsies presenting CIS were investigated by means of immunohistochemistry, using a polyclonal antibody against placental-alkaline phosphatase to detect CIS cells and a monoclonal antibody against human cytokeratin 18 to show expression of cytokeratin 18 intermediate filaments in Sertoli cells. RESULTS: All tubules bearing CIS showed positive cytokeratin expression of Sertoli cells if tubules were devoid of normal germ cells. However, a total of 13 specimen revealed CIS cells together with normal germ cells. In the presence of CIS cells together with round or elongated spermatids, adjacent Sertoli cells did not express cytokeratin immunoreactivity. In the case of combined presence of CIS and spermatogonia and primary spermatocytes, Sertoli cells could be found either immunopositive or immunonegative, and were positive in tubules with CIS and spermatogonia only. CONCLUSIONS: Sertoli cells associated with CIS cells undergo a process of dedifferentiation, seen by the re-expression of cytokeratin intermediate filaments. We suggest that this dedifferentiation results in a loss of Sertoli cell function and leads to a cessation of spermatogenic activity. 相似文献
2.
The diel 'activity', i.e. availability, of Ixodes ricinus larvae, nymphs and adults was investigated in a meadow and a forest habitat near Stockholm during 1991-1993. Generally, the immature ticks were more prevalent in the forest than in the meadow. In the meadow, the mean larval and adult numbers varied significantly between 4 h time intervals with the peak activity from 2300 to 0300 h. In the forest, the tick numbers did not differ significantly between the time intervals. The association of the tick activity with certain meteorological variables was strongest in the meadow, where the mean numbers of all tick stages were negatively correlated with the temperature. The relative humidity was positively correlated only with the mean numbers of larvae. In contrast, the larval activity in the forest was positively and negatively correlated with the temperature and relative humidity, respectively, while the nymphal and adult activity showed no association with these climatic variables. The impact of the host activity on the tick diel activity is also discussed. 相似文献
3.
DA O'Farrell HM Ridha P Keenan FW McManus M Stephens 《Canadian Metallurgical Quarterly》1997,28(5-6):377-379
Roller blading is a new and increasingly popular leisure activity in many countries. We reviewed 110 consecutive patients with roller-blade injuries between 1 January and 30 June 1996. The patients ranged from 4 to 14 years in age (mean 6.5 years). Eighty-three (75.4%) sustained injuries to the upper limb and 27 (24.5%) injured the lower limb. Fifty-six patients, were girls and 54 were boys. Of the 110 patients, 79 (72.7%) sustained fractures, 28 (25.4%) soft tissue injuries and 3 (2.7%) dislocations. Eighty-three (75.4%) of the patients wore no protective equipment on the limbs. Four months following injury 103 (93.6%) patients were fully recovered. The mean duration of school absence was 3 days. Subsequently 101 children returned to using roller-blades following injury. Seventy-three (66.3%) of these now use protective equipment. We found that injuries were unrelated to age or duration of roller-blading experience or to the brand-name of roller blades used, and that most of our patients wore no protective equipment at the time of injury. 相似文献
4.
PE Borchardt SM Quadri RS Freedman HM Vriesendorp 《Canadian Metallurgical Quarterly》1997,44(3):283-293
Sensory-perceptual abnormalities in people with autism are discussed from two perspectives: published firsthand accounts and existing psychological research evidence. A range of abnormalities, including hyper- and hyposensitivity, sensory distortion and overload, and multichannel receptivity and processing difficulties, are described in firsthand accounts and frequently portrayed as central to the autistic experience. A number of dangers are inherent in uncritically accepting these accounts at face value and in any wider generalization to the autistic population as a whole. Evidence from clinical studies suggests that unusual sensory responses are present in a majority of autistic children, that they are manifested very early in development, and that they may be linked with other aspects of autistic behavior. In addition, experimental studies using a range of indices have found evidence of unusual responses to sensory stimuli in autistic subjects. However the clinical and experimental research to date suffers from serious methodological limitations and more systematic investigation is warranted. Key issues for future psychological research in the area are identified. 相似文献
5.
6.
7.
8.
HM Krumholz Y Wang EM Parent J Mockalis M Petrillo MJ Radford 《Canadian Metallurgical Quarterly》1997,157(19):2242-2247
9.
E Kievit FB van Gog HM Schlüper GA van Dongen HM Pinedo E Boven 《Canadian Metallurgical Quarterly》1997,38(4):813-823
The effects of arginine vasopressin (AVP) and oxytocin (OT) upon thyroid-stimulating hormone (TSH), free thyroxine (FT4) and free triiodothyronine (FT3) release were studied in euthyroid rats. Intracerebroventricular (i.c.v.) infusion of AVP in doses of 0.5 ng or 5 ng led to significant increases in plasma levels of TSH as well as FT4 and FT3. The effects of OT injected i.c.v. in similar doses were not consistent (there was no parallel between the changes of respective hormones plasma levels). It may be concluded that vasopressin modulate the pituitary-thyroid system function; AVP is probably a physiological stimulator of TSH and thyroid hormones secretion. 相似文献
10.
The consumer health plan value survey: round two 总被引:2,自引:0,他引:2