全文获取类型
收费全文 | 3768篇 |
免费 | 362篇 |
专业分类
4130篇 |
出版年
2022年 | 22篇 |
2021年 | 52篇 |
2019年 | 42篇 |
2018年 | 44篇 |
2017年 | 42篇 |
2016年 | 61篇 |
2015年 | 123篇 |
2014年 | 107篇 |
2013年 | 143篇 |
2012年 | 232篇 |
2011年 | 242篇 |
2010年 | 141篇 |
2009年 | 137篇 |
2008年 | 203篇 |
2007年 | 227篇 |
2006年 | 235篇 |
2005年 | 197篇 |
2004年 | 227篇 |
2003年 | 198篇 |
2002年 | 196篇 |
2001年 | 45篇 |
2000年 | 26篇 |
1999年 | 37篇 |
1998年 | 52篇 |
1997年 | 44篇 |
1996年 | 47篇 |
1995年 | 33篇 |
1994年 | 45篇 |
1993年 | 28篇 |
1992年 | 28篇 |
1991年 | 24篇 |
1990年 | 19篇 |
1988年 | 20篇 |
1986年 | 29篇 |
1985年 | 28篇 |
1984年 | 42篇 |
1983年 | 31篇 |
1982年 | 51篇 |
1981年 | 40篇 |
1980年 | 36篇 |
1979年 | 31篇 |
1978年 | 25篇 |
1977年 | 26篇 |
1976年 | 30篇 |
1975年 | 29篇 |
1974年 | 26篇 |
1973年 | 29篇 |
1971年 | 19篇 |
1969年 | 20篇 |
1968年 | 19篇 |
排序方式: 共有4130条查询结果,搜索用时 0 毫秒
51.
52.
53.
Eugene C. Weinstein 《The Western journal of medicine》1965,102(6):416-418
Acute appendicitis still is a cause of considerable morbidity and now and then of death. The diagnostic accuracy in 316 patients operated on for acute appendicitis at Holy Cross Hospital was 76 per cent. In 24 of 239 cases of proved acute appendicitis, perforation had occurred, and the morbidity in those cases was three times that in the cases without perforation. Review of the cases did not reveal any clear-cut diagnostic criteria that might be used to predict perforation.A study of 30 patients with mesenteric lymphadenitis who were inadvertently operated on in the belief they had appendicitis, revealed that this condition is most likely to occur in young females with only a slight increase in the number of leukocytes. Although positive diagnosis of acute appendicitis is a difficult problem, the morbidity associated with needless operation is so much less than that which occurs in acute perforated appendicitis, that prompt exploration in any questionable case seems warranted. 相似文献
54.
A reagent composed of 0.2% p-phenylenediamine in 2 N NH4OH was used for the cytochemical demonstration of arbutin in plant tissue. Sections of fresh tissue were cut at 25-50 μ, mounted in a drop of the reagent, and allowed to stand uncovered 15-20 min before applying a coverslip. Arbutin stained dark blue to dark purple and was easily distinguished from other constituents of the cell, such as chlorogenic acid, isochlorogenic acid, caffeic acid, and quinic acid, which stained yellow, yellow-green, red or brown in color. The limit of sensitivity of the p-phenylenediamine-arbutin reaction was 1:100,000, as determined by spot-plate tests. 相似文献
55.
Susan Kent Eugene D. Weinberg Patricia Stuart-Macadam 《Human nature (Hawthorne, N.Y.)》1990,1(1):53-79
Mild hypoferremia represents an aspect of the ability of the body to withhold iron from pathogenic bacteria, fungi, and protozoa, and from neoplastic cells. However, our iron-withholding defense system can be thwarted by practices that enhance iron overload such as indiscriminate iron fortification of foods, medically prescribed iron supplements, alcohol ingestion, and cigarette smoking. Elevated standards for normal levels of iron can be misleading and even dangerous for individuals faced with medical insults such as chronic infection, neoplasia, cardiomyopathy, and arthritis. We are becoming increasingly aware that the wide-spread hypoferremia in human populations is a physiological response to insult rather than a pathological cause of insult, and that attempts to correct the condition by simply raising iron levels may not only be misguided but may actually impair host defense. 相似文献
56.
Akihiro Ohira Eugene de Juan Jr Yasuo Tano Charles A. Wilson 《The Histochemical journal》1996,28(9):607-611
Summary It has been proposed that basic fibroblast growth factor (basic FGF) mediates the neovascular response in a variety of conditions,
including diabetic retinopathy and branch retinal vein occlusion. To test the hypothesis that basic FGF was released from
retinal stores as a result of retinal ischaemia, transient retinal ischaemia was induced, followed by 48 h of reperfusion,
in the rat by combined central retinal vasculature and optic nerve ligation. The immunolocalization of basic FGF was studied
in the retina. We found that basic FGF in the normal retina is present around the deeper retinal vessels and in the neuronal
tissue of the outer plexiform layer. In the eyes that had ischaemia followed by reperfusion, there was moderate cellular oedema
with retinal swelling, and mitoses in the inner nuclear and plexiform layers. There were no changes evident at the immunohistochemical
level either in the intensity or distribution of stores of basic FGF. We conclude from these data that stores of basic FGF
are not altered dramatically under the conditions of transient experimental ischaemia and reperfusion in the rat, despite
the presence of cellular proliferation. 相似文献
57.
Patricia A. Lampe Ellen B. Cornbrooks Anna Juhasz Eugene M. Johnson James L. Franklin 《Developmental neurobiology》1995,26(2):205-212
Rat sympathetic neurons undergo programmed cell death (PCD) in vitro and in vivo when they are deprived of nerve growth factor (NGF). Chronic depolarization of these neurons in cell culture with elevated concentrations of extracellular potassium ([K+]o) prevents this death. The effect of prolonged depolarization on neuronal survival is thought to be mediated by a rise of intracellular calcium concentration ([Ca2+]i) caused by Ca2+ influx through voltage-gated channels. In this report we investigate the effects of chronic treatment of rat sympathetic neurons with thapsigargin, an inhibitor of intracellular Ca2+ sequestration. In medium containing a normal concentration of extracellular Ca2+ ([Ca2+]o), thapsigargin caused a sustained rise of intracellular Ca2+ concentration and partially blocked death of NGF-deprived cells. Elevating [Ca2+]o in the presence of thapsigargin further increased [Ca2+]i, suggesting that the sustained rise of [Ca2+]i was caused by a thapsigargin-induced Ca2+ influx. This treatment potentiated the effect of thapsigargin on survival. The dihydropyridine Ca2+ channel antagonist, nifedipine, blocked both a sustained elevation of [Ca2+]i and enhanced survival caused by depolarization with elevated [K+]o, suggesting that these effects are mediated by Ca2+ influx through L-type channels. Nifedipine did not block the sustained rise of [Ca2+]i or enhanced survival caused by thapsigargin treatment, indicating that these effects were not mediated by influx of Ca2+ through L-type channels. These results provide additional evidence that increased [Ca2+]i can suppress neuronal PCD and identify a novel method for chronically raising neuronal [Ca2+]i for investigation of this and other Ca2+-dependent phenomena. © 1995 John Wiley & Sons, Inc. 相似文献
58.
Eugene N. Kozloff 《Acta zoologica》1994,75(3):191-199
Abstract Adult orthonectids develop from germinal cells within a cytoplasmic matrix called a plasmodium. This is generally assumed to be formed by the parasite. In the case of Rhopalura ophiocomae, which lives in the brittle star Amphipholis squamata, the plasmodia occupying the perivisceral coelom are closely associated with the walls of the genital bursae or the gut, and they are covered by peritoneum. They have been reported to contain scattered small nuclei distinct from those within germinal cells, embryos, and adults, but the results of the present study indicate that such nuclei probably do not exist. Furthermore, electron micrographs show that some plasmodia are in continuity with the cytoplasm of contractile cells that lie beneath the peritoneum of a genital bursa or the gut of the host. The matrix of a plasmodium of R. ophiocomaeappears, therefore, to consist of cytoplasm of a contractile cell. It is proposed that after a contractile cell has been entered by an infective cell of the parasite, it hypertrophies, bulging progressively farther into the perivisceral coelom and lifting up the peritoneum, which remains in intimate contact with it. 相似文献
59.
Eugene S. Stevens 《Biopolymers》1994,34(10):1395-1401
The optical rotation of methyl 3-O -(α-D -mannopyranosyl)-α-D -mannopyranoside is calculated semiempirically as a function of the linkage dihedral angles ? (H1-C1-O1-C3′) and ψ (C1-O1-C3′-H3′). Comparison with the observed optical rotation in aqueous solution indicates the existence of at least two conformers in solution, which implies a degree of linkage flexibility. The result is in agreement with some, but not all, calculated potential energy surfaces, and with recently published nmr data. © 1994 John Wiley & Sons, Inc. 相似文献
60.
Eugene S. Stevens 《Biopolymers》1994,34(10):1403-1407
The optical rotation of methyl 2-O -(α-D -mannopyranosyl)-α-D -mannopyranoside is calculated semiempirically as a function of the linkage dihedral angles ? (H1-C1-O1-C2′) and ψ (C1-O1-C2′-H2′). Although the rotation calculated for the global energy minimum conformation found in several rigid-residue modeling calculations (?,ψ = ?40°,?20°) is in good agreement with the observed solution rotation, the observed rotation is also compatible with the limited flexibility inferred from more recent relaxed residue modeling calculations on a structurally related rhamnose disaccharide © 1994 John Wiley & Sons, Inc. 相似文献