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   638篇
  免费   62篇
  国内免费   1篇
  701篇
  2023年   8篇
  2021年   12篇
  2020年   11篇
  2019年   11篇
  2018年   9篇
  2017年   14篇
  2016年   18篇
  2015年   16篇
  2014年   12篇
  2013年   25篇
  2012年   21篇
  2011年   30篇
  2010年   17篇
  2009年   18篇
  2008年   26篇
  2007年   23篇
  2006年   23篇
  2005年   20篇
  2004年   12篇
  2003年   25篇
  2002年   15篇
  2001年   23篇
  2000年   17篇
  1999年   17篇
  1997年   8篇
  1996年   6篇
  1994年   7篇
  1992年   16篇
  1991年   12篇
  1990年   12篇
  1989年   9篇
  1988年   13篇
  1987年   8篇
  1985年   10篇
  1984年   6篇
  1983年   8篇
  1981年   8篇
  1979年   10篇
  1978年   8篇
  1977年   14篇
  1976年   8篇
  1974年   6篇
  1973年   6篇
  1971年   7篇
  1970年   7篇
  1968年   8篇
  1967年   6篇
  1966年   5篇
  1888年   6篇
  1887年   6篇
排序方式: 共有701条查询结果,搜索用时 0 毫秒
1.
2.
Two laboratories exchanged and rescreened a large sample of cases with cervicovaginal smears they had consecutively accessioned to examine the reproducibility of gynecologic cytodiagnosis under optimum conditions. At least a "working agreement" (diagnoses within +/- 1 category on a ten-category scale) was achieved in diagnoses of normal, benign reaction and squamous abnormality (from minimal dysplasia though invasive cancer) in 18,859 cases (96.8%), of endometrial abnormality in 21 cases (42%) and of "unsatisfactory" in 99 cases (20.7%). Larger differences occurred in greater than or equal to 30% of cases except in the categories of "normal" and "benign reaction," reaching a maximum of 82% for moderate dysplasia. Reexamining 382 cases decreased disagreement by category to the 20% to 65% range only in the five categories of dysplasia plus carcinoma in situ. Agreement was not predicated on the presence of endocervical cells or squamous metaplasia; the basis for "unsatisfactory" calls was not uniform. Comparison of the laboratories' diagnoses with referee diagnoses or, on 178 cases, with tissue diagnoses also demonstrated differences in diagnostic criteria.  相似文献   
3.
The purpose of these studies was to determine quantitatively the reflex cardiovascular responses to stimulation of the pulmonary C-fibers in dogs. We used a preparation in which the airway, pulmonary artery, and the pulmonary veins to the left lung were cannulated in situ. Ventilation and perfusion of the right lung maintained the animal in relatively normal homeostasis. Capsaicin, a decylenic acid amide of vanillylamine that selectively stimulates nerve endings of unmyelinated fibers (C-fibers), was injected into the left pulmonary artery in 5-ml boluses. Maximal reflex responses were obtained with concentrations as low as 0.8-1.6 X micrograms-1 X kg-1. Heart rate, hindlimb resistance, and left ventricular contractility were lowered transiently (the maximal responses showing declines of 40, 13, and 15.2%, respectively). As a result of these changes, combined with vasodilation in other resistance vessels, cardiac output fell 28% and blood pressure fell 35%. Interrupting the afferent neural pathway by severing the ipsilateral cervical vagus nerve eliminated these responses, confirming the distribution of their reflex origin. Although the role of these reflexes in homeostasis has not been decided, the results of this study suggest that the lungs of dogs, if appropriately stimulated, potentially can exert a major inhibitory influence on the neural regulation of cardiovascular function.  相似文献   
4.
Moens  P. B.  Ashton  M. L. 《Chromosoma》1985,91(2):113-120
Synaptonemal complex (SC) analysis of six laboratory yeast strains showed the SC karyotypes to be repeatable within strains. Chromosomal differences were found between strains. In five of the strains, two SCs insert into the nucleolus. This represents a single bivalent with a nucleolar organizer in a medial position as is suggested by genetic data or two bivalents each with a terminal nucleolar organizer. In the first interpretation, n=16; in the second, n=17. Strain Tris has a single nucleolar SC and n=17. In strains DCx374, DCx416 and x 8366a the genetically determined rearrangements of linkage group III could not be identified. Presumably the short SC (0.33 m) associated with linkage group III cannot accommodate an inversion loop or a translocation configuration. The strains however were found to harbour a reciprocal translocation involving the nucleolar chromosome. Trisomy for one of the longer chromosomes was observed in Tris and spo10. It is concluded that rearrangements of the medium and long but not short yeast chromosomes can be detected cytologically. — Measurements of nuclear volumes show SC length to vary with artifactually induced swelling of the nucleus. Linear regression of SC length over nuclear radius indicates that actual SC length is only about one-half the observed length. As a result the DNA packing per SC unit length is higher then previously estimated.  相似文献   
5.
6.
Hormonal control of proteinase activity in squash cotyledons   总被引:2,自引:1,他引:1       下载免费PDF全文
A crude proteolytic enzyme preparation which hydrolyzes casein was isolated from the cotyledons of squash seedlings. The presence of ethylene diamine tetraacetate or cysteine did not appreciably affect the activity of the preparation. During the course of germination, the level of proteolytic activity increased in the cotyledons of intact embryos through the third day and then decreased. The presence of the embryonic axis during the first 32 hours of germination was a prerequisite for the development of maximum proteolytic activity.  相似文献   
7.
P R Ashton 《Acta cytologica》1989,33(4):451-454
The data produced by membership surveys undertaken by the American Society for Cytotechnology that pertain to the quality diagnosis of Papanicolaou smears are reviewed. The results documented the parameters in such areas as workload, quality control, health and safety, continuing education, productivity measurement, reporting systems and salaries and helped to pinpoint problems in these areas. Some of these problems are being addressed through cooperative efforts with other groups concerned with improving the diagnostic accuracy of cytopathology.  相似文献   
8.
9.
alpha-L-Iduronidase activity is deficient in mucopolysaccharidosis type I (MPS I; Hurler syndrome, Scheie syndrome) patients and results in the disruption of the sequential degradation of the glycosaminoglycans dermatan sulfate and heparan sulfate. A monoclonal antibody-based immunoquantification assay has been developed for alpha-L-iduronidase, which enables the detection of at least 16 pg alpha-L-iduronidase protein. Cultured human skin fibroblasts from 12 normal controls contained 17-54 ng alpha-L-iduronidase protein/mg extracted cell protein. Fibroblasts from 23 MPS I patients were assayed for alpha-L-iduronidase protein content. Fibroblast extracts from one MPS I patient contained at least six times the level of alpha-L-iduronidase protein for normal controls--but contained no associated enzyme activity--and is proposed to represent a mutation affecting the active site of the enzyme. Fibroblast extracts from 11 MPS I patients contained 0.05-2.03 ng alpha-L-iduronidase protein/mg extracted cell protein, whereas immunodetectable protein could not be detected in the other 11 patients. Four fibroblast extracts with no immunodetectable alpha-L-iduronidase protein had residual alpha-L-iduronidase activity, suggesting that the mutant alpha-L-iduronidase in cultured cells from these MPS I patients has been modified to mask or remove the epitopes detected by two monoclonal antibodies used in the quantification assay. Both the absence of immunoreactivity in a mild MPS I patient and high protein level in a severe MPS I patient present limitations to the use of immunoquantification analysis as a sole measure of patient phenotype. Enzyme kinetic analysis of alpha-L-iduronidase from MPS I fibroblasts revealed a number of patients with either abnormal substrate binding or catalytic activity.(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   
10.
The neurite distribution of three large neurosecretory cells, namely one canopy cell and two lateral-lobe cells from each lateral lobe of the cerebral ganglia in Helisoma duryi were studied by thick and thin plastic serial sections. These cells from only the right lateral lobe innervate the dorsal body. Neurites from the canopy cell innervate the cell-bodies whereas those from the lateral-lobe cells innervate the cell-processes of the dorsal body. Neurosecretory granules from these neurites are released at their sites of innervation. The neurites of the optic nerve form synapses with lateral-lobe cell(1), and synapse-like contacts with lateral-lobe cell(2) while a neurite of each canopy cell is found within its collateral optic nerve. Based on the anatomy of the lateral-lobe nerve cells and the optic nerve, it is argued that the stimulatory effect of long days on the dorsal body and on egg production is mediated through the lateral-lobe cells and the canopy cell.  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