全文获取类型
收费全文 | 29431篇 |
免费 | 1395篇 |
国内免费 | 11篇 |
专业分类
30837篇 |
出版年
2016年 | 254篇 |
2015年 | 482篇 |
2014年 | 484篇 |
2013年 | 1160篇 |
2012年 | 847篇 |
2011年 | 783篇 |
2010年 | 633篇 |
2009年 | 689篇 |
2008年 | 778篇 |
2007年 | 820篇 |
2006年 | 732篇 |
2005年 | 779篇 |
2004年 | 662篇 |
2003年 | 614篇 |
2002年 | 663篇 |
2001年 | 316篇 |
2000年 | 286篇 |
1999年 | 306篇 |
1998年 | 291篇 |
1997年 | 231篇 |
1996年 | 303篇 |
1995年 | 287篇 |
1994年 | 239篇 |
1993年 | 394篇 |
1992年 | 369篇 |
1991年 | 389篇 |
1990年 | 387篇 |
1989年 | 567篇 |
1988年 | 515篇 |
1987年 | 601篇 |
1986年 | 533篇 |
1985年 | 498篇 |
1984年 | 446篇 |
1983年 | 374篇 |
1982年 | 420篇 |
1981年 | 469篇 |
1980年 | 424篇 |
1979年 | 451篇 |
1978年 | 484篇 |
1977年 | 527篇 |
1976年 | 527篇 |
1975年 | 553篇 |
1974年 | 430篇 |
1973年 | 297篇 |
1972年 | 281篇 |
1971年 | 261篇 |
1970年 | 283篇 |
1969年 | 234篇 |
1968年 | 215篇 |
1964年 | 224篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
901.
Seven microbial peptide inhibitors—chymostatin, antipain, elastatinal, leupeptin, pepstatin, bestatin, and phosphoramidon—were tested for their efficiency to inhibit thermitase, a thermostable serine protease fromThermoactinomyces vulgaris. Chymostatin and antipain were the most effective inhibitors, with Ki values of 7×10–8
M and 2×10–7
M, respectively. Except for leupeptin, all inhibitors resist hydrolysis by thermitase. Leupeptin, however, is cleaved by thermitase between the two leucylresidues. Further, a close relationship in specificity between thermitase and subtilisin BPN and their distinct discrimination from elastase specificity was demonstrated by using these inhibitors. 相似文献
902.
Dr. Edward B. Blanchard Guy C. McCoy Frank Andrasik Maryrose Acerra Thomas P. Pallmeyer Robert Gerardi Mindy Halpern Alison Musso 《Applied psychophysiology and biofeedback》1984,9(4):471-495
In a controlled trial, thermal biofeedback (n=20) and abbreviated progressive relaxation (n=22) were compared in the treatment of mild to moderate hypertensive patients whose blood pressures (BP) were initially controlled on two medications. For the clinical end point of maintaining control of BP on a single drug after treatment, biofeedback was superior to relaxation training (at 3 months, 47% success for biofeedback versus 23% for relaxation). This same result tended to be true for patient-measured home BPs. BPs from laboratory psychophysiological testing showed no consistent advantage for one treatment over the other.This research was supported by a grant from NHLB1, HL-27622. 相似文献
903.
Renata Brelińska Prof. Dr. Christoph Pilgrim Ingrid Reisert 《Cell and tissue research》1984,236(3):661-667
Summary Male Wistar rats were injected intravenously with 5-(3H)uridine-labeled lymphocytes isolated from lymph nodes of syngeneic donors and enriched in T cells. After short periods of time (3 to 120 min after injection), labeled lymphocytes were localized in spleen compartments using autoradiography to identify routes of lymphocyte movement from blood into splenic parenchyma and to follow migration pathways of recirculating lymphocytes within the periarterial lymphoid sheath (PALS). Topographical analysis of labeled lymphocytes was performed in specific planes of PALS characterized by the diameter of the arterial vessel and termed PALS large, PALS medium, and PALS small (PALS L, PALS M, PALS S, respectively). Attention was also paid to accumulations of labeled lymphocytes close to the arterial vessel wall. Initially, labeled lymphocytes were localized in PALS S and PALS M near the terminal branching of arterial vessels and in the marginal zone (MZ). We conclude that lymphocytes emigrate from blood into splenic parenchyma within two white pulp compartments: in MZ, and directly within PALS through the wall of capillary vessels. The sequential accumulation of labeled cells near arterial vessels of increasing diameter suggests that the recirculating pool of lymphocytes migrates into the central part of PALS L by two routes: from MZ, and along arterial vessels from PALS S and PALS M.R.B. was a fellow of the Alexander von Humboldt-Stiftung, on leave from the Department of Histology and Embryology, Institut of Biostructure, Academy of Medicine, ul. Swiecickiego 6, PL-60-781 Pozna, Poland. 相似文献
904.
Summary Wound repair and proliferation were examined in the injured newt atrium with light- and electron-microscopic techniques including autoradiography. Hearts were injured by removing a piece approximately 0.5 mm2 of the atrial wall. The five-day wound was an endothelial and mesothelial-lined blood clot bordered by a 150-m necrotic zone. Repair progressed from the periphery inward with areas of macrophage activity replaced by fibroblasts and connective tissue. The wound at 25 days consisted of a scar with few myocytes. There was no difference in the proliferative behavior between the right and left atria. Proliferative cells were localized to a 500-m reactive zone surrounding the wound. The maximum mesothelial cell thymidine-labeling index of 20.5% and mitotic index of 1.4% were seen 5 days after injury. The peak connective tissue cell thymidine-labeling index of 10.2% and mitotic index of 0.4% were seen 10 days after wounding. The peak thymidine-labeling index of 9.8% for myocardial cells was recorded 10 days after injury with a mitotic index of 0.2%. Proliferation returned to control levels by 25 days post-injury. Electron microscopy demonstrated that myocytes engaged in DNA synthesis were indistinguishable from control myocytes. Z-band material was not observed in mitotic myocytes, but myofilaments and junctions were present. 相似文献
905.
The fate of 15NH
inf4
sup+
and 15NOinf3− was followed in control and PO
inf4
sup3−
enriched 1570 l mesocosms filled with epilimnetic water from an oligotrophic Rocky Mountain lake. Volumetric incorporation
of 15NH
inf4
sup+
and 15NO
inf3
sup−
into phytoplankton and bacterioplankton (particulates between 280 and 0.7 μm), and crustacean zooplankton > 80 μm was enhanced
by PO
inf4
sup3−
, but no increase in biomass specific rates of uptake by phytoplankton and bacteria occurred for either form of 15N. Dilution of both 15NH
inf4
sup+
and 15NO
inf3
sup−
by 14NH
inf4
sup+
and 14NO
inf3
sup−
, respectively, was evident indicating regeneration of these nutrients, but regeneration rates were not effected by PO
inf4
sup3−
enrichment. The results illustrate the strong trophic coupling between N dynamics and PO
inf4
sup3−
enrichment in this system. 相似文献
906.
The effect of a number of compounds structurally related to glutamic acid and other nitrogenous compounds on the composition of three forms of glutamine synthetase (GS) inRhizobium phaseoli has been examined in detail. Amino acids like glutamic acid, glutamine, and a fixed source of nitrogen like ammonium chloride did not alter the relative glutamine synthetase composition.l-Methioninedl-sulfoximine (MSX), a glutamate analogue, significantly repressed the synthesis of GSIII to a greater extent.,N-oxalyl,-diaminopropionic acid (ODAP), another glutamate analogue, selectively stimulated the synthesis of GSII, and the effect of ODAP on GSII synthesis was greatly enhanced in the presence of ethylenediamine or ammonium chloride. Ethylenediamine itself caused a predominant synthesis of GSIII.-Cyanoalanine-grownR. phaseoli did not synthesize GSI. The synthesis of the three different glutamine synthetases can thus be differentially modulated. 相似文献
907.
Kirsten M. Madsen C. William Applegate Dr. C. Craig Tisher 《Cell and tissue research》1982,226(2):363-374
Summary Morphological examination of kidney biopsies from patients with glomerulonephritis and hematuria has revealed the presence of erythrocytes within epithelial cells of the proximal tubule. This observation suggested that the proximal tubule might be capable of phagocytizing morphologically intact erythrocytes. To examine this possibility small quantities of heparinized autologous blood were injected into surface convolutions of proximal tubules of the rat kidney using standard micropuncture techniques. At time intervals ranging from 10 min to 120 h after injection, the kidneys were preserved for light and transmission electron microscopy by drip-fixation with a half-strength Karnovsky's glutaraldehyde-formaldehyde fixative.During the initial 6 h there was a flattening of the brush border and accumulation of electron-dense material representing hemoglobin in apical vacuoles and in lysosome-like structures. From 6 to 15 h after micropuncture, there was progressive loss of the brush border and the simultaneous formation of pseudopodia-like evaginations that extended from the apical plasma membrane and surrounded the individual erythrocytes. By 18 and 24 h, erythrocytes were observed in the proximal tubule cells. At later time intervals, edema, lymphocytic infiltration, and fibrosis were observed in the interstitium. In addition, crystalline structures were present in the lumen and the cells of both proximal and distal tubules. These findings suggest that in addition to their well-established ability to pinocytize hemoglobin and other proteins, the cells of the proximal tubule are capable of phagocytizing morphologically intact autologous erythrocytes. It is possible that phagocytosis by the proximal tubule cells may play a role in the disposal of erythrocytes from the tubular fluid in hematuric conditions. 相似文献
908.
Walter A. Heidmann Annegret Büthe Martin Beyerbach Reinhard Löhmer und Harald A. Rüssel-Sinn 《Journal of Ornithology》1989,130(3):311-320
Zusammenfassung Rückstände chlorierter Kohlenwasserstoffe in Eiern und Lebern von im Binnenland Niedersachsens brütenden Vogelarten — Feldsperling, Mehlschwalbe, Weißstorch, Graureiher, Saatkrähe, Stockente und andere Arten — werden angegeben und deren Abhängigkeit von Brutort, Nahrung und Zugverhalten diskutiert.
Chlorinated hydrocarbons of some bird species breeding in the inland of Lower Saxony (FRG)
Summary Residues of chlorinated hydrocarbons in eggs and livers of some bird species — Tree Sparrow, House Martin, White Stork, Heron, Rook, Mallard, and further species — are presented. The dependence on place of breeding, food web, and migration is discussed.相似文献
909.
Yoshiya Shigematsu Ken Tsukahara Tomoaki Tanaka Michio Takeuchi Dr. Eiji Ichishima 《Current microbiology》1986,13(1):43-46
The molecular properties, such as molecular weight, N-and C-terminal amino acids, amino acid composition, and circular dichroism, of 1,2--mannosidase isolated from the culture filtrate ofAspergillus saitoi were determined.The enzyme had aK
m of 0.67 mM andk
cat of 1.27/s with mannobiose at pH 50.0 and 30°C. The anomeric configuration of the reaction products of the enzyme was examined by studying the -anomer. A single Manl2Man linkage in intact Taka-amylase A fromAspergillus oryzae was hydrolyzed, producing free mannose. 相似文献
910.
Ascites from patients with metastatic ovarian carcinoma contains high amounts of an activity that increases vascular permeability, as easily detected by a rat skin test. Ascites was fractionated by gel permeation and reversed-phase high-performance liquid chromatographies. The fractions were analysed for permeability-increasing activity. In this way a peptide was isolated and identified as Ile-Ser-bradykinin by sequence and amino-acid analyses. It is identical with T-kinin which has previously been detected as a product of an acute-phase protein, T-kininogen, in rats but never in human material. The so far identified human kininogens, i.e. high- and low-molecular mass kininogens, can only release Met-Lys-bradykinin or its degradations products, as Ile-Ser-bradykinin is not a part of their structure. However, the present results provide evidence that the permeability factor Ile-Ser-bradykinin under certain conditions can be produced in considerable amounts also by human tissues. 相似文献