全文获取类型
收费全文 | 3381篇 |
免费 | 275篇 |
专业分类
3656篇 |
出版年
2021年 | 24篇 |
2020年 | 21篇 |
2019年 | 25篇 |
2018年 | 36篇 |
2017年 | 28篇 |
2016年 | 54篇 |
2015年 | 105篇 |
2014年 | 113篇 |
2013年 | 144篇 |
2012年 | 170篇 |
2011年 | 193篇 |
2010年 | 127篇 |
2009年 | 129篇 |
2008年 | 176篇 |
2007年 | 207篇 |
2006年 | 150篇 |
2005年 | 154篇 |
2004年 | 158篇 |
2003年 | 172篇 |
2002年 | 168篇 |
2001年 | 49篇 |
2000年 | 27篇 |
1999年 | 46篇 |
1998年 | 51篇 |
1997年 | 24篇 |
1996年 | 39篇 |
1995年 | 38篇 |
1994年 | 30篇 |
1993年 | 40篇 |
1992年 | 30篇 |
1991年 | 36篇 |
1990年 | 23篇 |
1989年 | 32篇 |
1988年 | 32篇 |
1987年 | 30篇 |
1986年 | 25篇 |
1985年 | 35篇 |
1984年 | 32篇 |
1983年 | 36篇 |
1982年 | 35篇 |
1981年 | 37篇 |
1980年 | 35篇 |
1979年 | 28篇 |
1978年 | 39篇 |
1977年 | 24篇 |
1976年 | 19篇 |
1974年 | 27篇 |
1973年 | 49篇 |
1972年 | 19篇 |
1971年 | 26篇 |
排序方式: 共有3656条查询结果,搜索用时 0 毫秒
31.
A new simple and sensitive in-vitro method for the diagnosis of type 1 (IgE-mediated) hypersensitivity in man is described. Sliced human skin is passively sensitized by reaginic serum from allergic patients and the presence of antigen-specific IgE on the sensitized slices is detected by assay of antigen-evoked histamine release. Serum from 12 out of 14 patients with clinical respiratory allergy and positive skin tests gave significant antigen-specific histamine release. This method, which is essentially an in-vitro model of the Prausnitz-Küstner reaction, should prove of value in the diagnosis of human reaginic hypersensitivity in man. 相似文献
32.
Serial sections of the rectal valve in Aphelenchoides blastophthorus Franklin and the oesophago-intestinal valve in Thornenema wickeni Yeates were examined electron microscopically. Each valve when closed appears as a convoluted path of closely apposed (10 nm) pairs of three-layered cell membranes. Both valves serve to stop intestinal leakage, open briefly and rapidly by forcible dilatation and are closed by pressure from surrounding tissues, helped perhaps by intermolecular forces. 相似文献
33.
Timex, a strain of Neurospora crassa which exhibits a circadian rhythm of conidia formation in growth-tube cultures, has been found to differ from wild-type strains by two genes. One gene, inv, is responsible for an invertase deficiency, whereas the second gene, bd, is of unknown function. Both genes map independently from other genes known to induce Neurospora rhythmicity. The inv gene is not essential for the timex phenotype because bd strains express that phenotype on certain media. Although inv strains do exhibit some rhythmicity of their own, the rhythmicity apparently is not a direct result of the invertase deficiency, since there is no correlation between invertase level and rhymicity in 29 strains tested. Of the 29 strains tested, 20 exhibited some rhythmicity in growth-tube cultures, suggesting that morphological manifestations of rhythmicity in Neurospora may result from the function or the loss of function of numerous genes, or both. There was no correlation in these strains between rhythmicity and (i) genetic background; (ii) geographical origin; or (iii) nutritional requirements. 相似文献
34.
35.
36.
Summary The marine blue green alga, Trichodesmium erythraeum, was studied with electron microscopy in an attempt to elucidate the structural basis for its rapid lysis when removed from its marine environment. In this connection, it was found that a thining of the electron-dense layer of the longitudinal wall at the site adjacent to transverse wall attachment was responsible for lysis. The underlying biochemical basis for this change has not been elucidated because of the extreme difficulties of maintaining and growing the alga in culture under defined conditions. Several other features of considerable interest also were found. Especially interesting is the very regular array of gas vacuoles in the form of a hollow cylinder which shields most of the photosynthetic system. It was suggested that the gas vacuoles might possibly function optically, having adaptive value in protecting the free-floating alga from excessive radiation. In addition, a detailed structure of the cylindrical bodies was presented, and its structure with the photosynthetic lamellae was compared. On the basis of sectoring to form fragments of double lamellar units from the cylindrical body which are identical in structure to the photosynthetic lamellae, it has been postulated that the cylindrical body may be the site of synthesis for the photosynthetic system in Trichodesmium erythraeum. 相似文献
37.
A spontaneous, single-gene mutation responsible for a total lack of invertase activity in Neurospora crassa is described. The mutation is believed to lie in the structural gene for invertase, since an immunologically cross-reacting protein is made by the mutant strain. In addition, there was no evidence for a defect in regulation of invertase activity or synthesis by the following criteria. (i) The invertaseless condition was recessive in heterokaryons; (ii) no invertase inhibitor was found in mutant extracts by mixing experiments; and (iii) none of the several sugars able to induce activity in wild-type strains was able to induce activity in the mutant strain. It was also discovered that most of the wild-type enzyme (55 to 75%) cannot be washed free from the rapidly sedimenting cell debris. This finding provided additional support for the hypothesis that Neurospora invertase is located within or about the cell wall. 相似文献
38.
Malcolm M. Mc Henry 《The Western journal of medicine》1968,108(3):179-187
Cardiac monitoring facilities have been present in teaching hospital centers for over five years. A substantial decrease in mortality has been observed in monitored patients with acute myocardial infarction. The community hospital system offers a challenge to effective monitoring since many physicians care for patients and often many kinds of therapy are used.After 18 months of operation mortality from myocardial infarction was only 16.6 percent in a community hospital monitoring unit where the majority of the emergency care and resuscitation was carried out by nurses. Vital to this success was the use of standing orders for nurses, requirement of privilege to practice within the monitoring facility and acceptance of the nurse as a therapist in emergency situations.Fourteen patients were successfully resuscitated and were later discharged from the hospital. Four of them had ventricular fibrillation from digitalis intoxication.Patients with shock and severe congestive heart failure continue to be a major unsolved clinical problem. The results indicate that the potentially viable patient with serious electrical disturbances can almost invariably be salvaged. 相似文献
39.
Malcolm R. Powell 《The Western journal of medicine》1968,108(6):412-422
The Anger scintillation camera greatly broadens the range of studies performed by radioisotope imaging devices. Its ability to view in any direction, to make an image simultaneously of an entire field of view, and to obtain images rapidly, all serve to make scintiphotography analogous to fluoroscopy. Illustrations of its uses in static and dynamic gammaphotography and in numerical data processing are described. 相似文献
40.
Malcolm S. M. Watts 《The Western journal of medicine》1964,101(6):417-421
The Committee to Study the Role of Medicine of the California Medical Education and Research Foundation (CMERF) is grateful to Dr. Watts for the following paper which served as the philosophical basis for the Committee''s study and discussions. The Committee is also grateful to CMERF and to its president, James C. Doyle, for the encouragement and cooperation it has received in the course of its intensive study of a problem which is of great interest and concern to the medical profession of California.Dr. Watts'' background paper has served as a potent stimulus in directing the Committee''s attention to the continuing dialogue between medicine and society, and in focussing on problems and issues which will be the subject of the Committee''s Second Progress Report, excerpts from which are scheduled for publication in the next issue of California Medicine. 相似文献