全文获取类型
收费全文 | 739377篇 |
免费 | 82207篇 |
国内免费 | 420篇 |
出版年
2018年 | 10952篇 |
2017年 | 10670篇 |
2016年 | 11232篇 |
2015年 | 11260篇 |
2014年 | 12876篇 |
2013年 | 18500篇 |
2012年 | 22557篇 |
2011年 | 26901篇 |
2010年 | 19052篇 |
2009年 | 17784篇 |
2008年 | 23306篇 |
2007年 | 25329篇 |
2006年 | 17925篇 |
2005年 | 18221篇 |
2004年 | 17269篇 |
2003年 | 17170篇 |
2002年 | 16790篇 |
2001年 | 33782篇 |
2000年 | 34309篇 |
1999年 | 26742篇 |
1998年 | 8905篇 |
1997年 | 9605篇 |
1996年 | 9115篇 |
1995年 | 8472篇 |
1994年 | 8381篇 |
1993年 | 8384篇 |
1992年 | 22505篇 |
1991年 | 22123篇 |
1990年 | 21212篇 |
1989年 | 20653篇 |
1988年 | 19017篇 |
1987年 | 18131篇 |
1986年 | 16845篇 |
1985年 | 16723篇 |
1984年 | 13808篇 |
1983年 | 11900篇 |
1982年 | 9098篇 |
1981年 | 8060篇 |
1980年 | 7625篇 |
1979年 | 13135篇 |
1978年 | 10234篇 |
1977年 | 9336篇 |
1976年 | 8662篇 |
1975年 | 9735篇 |
1974年 | 10100篇 |
1973年 | 9958篇 |
1972年 | 9551篇 |
1971年 | 8532篇 |
1970年 | 7018篇 |
1969年 | 6731篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
In this paper we describe the use of punched feature cards in a general practice for 18 months. Its advantages are the low cost, speed of information retrieval, visible statistics, computer compatibility, accuracy, confidentiality, flexibility, and simplicity of setting up and collection of information. The system encourages the doctor to ask questions about his practice, and could readily be adopted in other practices. 相似文献
992.
993.
Antigen-induced production of migration inhibitory factor (MIF) by sensitized lymphocytes requires macrophages to effectively stimulate lymphocytes with soluble antigen in vitro. The present study showed that macrophage-depleted lymphocytes of sensitized guinea pigs could be activated with antigens when the culture supernatant of peritoneal adherent cells pulse-stimulated with a macromolecular fraction of bacterial lipopolysaccharide (LPS) was added to the lymphocyte culture. The apparent macrophage-replacing activity was found in the fraction which emerged slightly ahead of serum albumin upon gel filtration of the culture supernatant, and the activity was shown to be destroyed by heating at 65 °C for 30 min or by trypsin digestion. These results appeared to show that the activity was due to a protein component, most probably released from macrophages. Two-step culture experiments revealed that the soluble factor should be present in the early stage of the culture to activate the macrophage-depleted immune lymphocytes with antigen, as well as in the later stage when the presence of antigen in the medium is no longer required. Furthermore, the factor was shown to act in the activation of a T-cell-enriched fraction of immune lymphocytes. The factor appeared to be playing some essential role in making an antigenic stimulus effective for the activation of immune lymphocytes. 相似文献
994.
Divergence time estimates of mammals from molecular clocks and fossils: Relevance of new fossil finds from India 总被引:1,自引:0,他引:1
G. V. R. Prasad 《Journal of biosciences》2009,34(5):649-659
This paper presents a brief review of recent advances in the classification of mammals at higher levels using fossils and
molecular clocks. It also discusses latest fossil discoveries from the Cretaceous — Eocene (66–55 m.y.) rocks of India and
their relevance to our current understanding of placental mammal origins and diversifications. 相似文献
995.
A. -M. Neghina A. Anghel I. Sporea A. Popescu R. Neghina A. Collins K. Thorstensen 《Journal of applied genetics》2009,50(2):173-176
The present study aimed at assessing the frequency ofHFE mutations (C282Y, H63D and S65C) in western Romanian patients with liver disease of diverse aetiologies suspected of iron
overload. A total of 21 patients, all Romanian residents hospitalized with clinical suspicion of iron overload and liver disease,
were assayed for C282Y, H63D and S65C mutations, serum ferritin and viral hepatitis markers. Overall, 9 out of the 21 patients
(42.86%) were found to harbour mutations in theHFE gene: 4 homozygotes C282Y (19.0%), 1 compound heterozygote C282Y/H63D (4.8%), 1 single heterozygote C282Y (4.8%), 2 single
heterozygotes H63D (9.5%), 1 single heterozygote S65C (4.8%), and 12 wild-type cases (57.1%). Among the subgroup of 10 patients
with the most prominent signs of iron overload (hyperferritinaemia and/or hepatocyte iron score ≥ 1), without hepatocellular
carcinoma, theHFE genotypes were conclusive in 5 cases (50%). They had significantly increased ferritin levels compared to wild-type cases
(P = 0.029). The inclusion of iron studies during routine clinical visits, coupled with the availability ofHFE genotyping for family and population studies, should facilitate the early detection of hereditary haemochromatosis in Romania. 相似文献
996.
Stem cell function during plant vascular development 总被引:1,自引:0,他引:1
A. Elo J. Immanen K. Nieminen Y. Helariutta 《Seminars in cell & developmental biology》2009,20(9):1097-1106
While many regulatory mechanisms controlling the development and function of root and shoot apical meristems have been revealed, our knowledge of similar processes in lateral meristems, including the vascular cambium, is still limited. Our understanding of even the anatomy and development of lateral meristems (procambium or vascular cambium) is still relatively incomplete, let alone their genetic regulation. Research into this particular tissue type has been mostly hindered by a lack of suitable molecular markers, as well as the fact that thus far very few mutants affecting plant secondary development have been described. The development of suitable molecular markers is a high priority in order to help define the anatomy, especially the location and identity of cambial stem cells and the developmental phases and molecular regulatory mechanisms of the cambial zone. To date, most of the advances have been obtained by studying the role of the major plant hormones in vascular development. Thus far auxin, cytokinin, gibberellin and ethylene have been implicated in regulating the maintenance and activity of cambial stem cells; the most logical question in research would be how these hormones interact during the various phases of cambial development. 相似文献
997.
998.
999.
J L Bowtell K Gelly M L Jackman A Patel M Simeoni M J Rennie 《Journal of applied physiology》2000,88(5):1529-1536
Seven untrained male subjects participated in a double-blind, crossover study conducted to determine the efficacy of different carbohydrate drinks in promoting carbohydrate storage in the whole body and skeletal muscle during recovery from exhaustive exercise. The postabsorptive subjects first completed an exercise protocol designed to deplete muscle fibers of glycogen, then consumed 330 ml of one of three carbohydrate drinks (18.5% glucose polymer, 18.5% sucrose, or 12% sucrose; wt/vol) and also received a primed constant infusion of [1-(13)C]glucose for 2 h. Nonoxidative glucose disposal (3.51 +/- 0.28, 18.5% glucose polymer; 2.96 +/- 0.32, 18.5% sucrose; 2.97 +/- 0.16, 12% sucrose; all mmol. kg(-1). h(-1)) and storage of muscle glycogen (5.31 +/- 1.11, 18.5% glucose polymer; 4.07 +/- 1.05, 18.5% sucrose; 3.45 +/- 0.85, 12% sucrose; all mmol. kg wet wt(-1). h(-1); P < 0.05) were greater after consumption of the glucose polymer drink than after either sucrose drink. The results suggest that the consumption of a glucose polymer drink (containing 61 g carbohydrate) promotes a more rapid storage of carbohydrate in the whole body, skeletal muscle in particular, than an isoenergetic sucrose drink. 相似文献
1000.
The Capricorn silvereye (Zosterops lateralis chlorocephalus) is ideally suited to investigating the genetic basis of body size evolution. We have isolated and characterized a set of microsatellite markers for this species. Seven out of 11 loci were polymorphic. The number of alleles detected ranged from two to five and observed heterozygosities between 0.12 and 0.67. One locus, ZL49, was found to be sex‐linked. This moderate level of diversity is consistent with that expected in an isolated, island population. 相似文献