全文获取类型
收费全文 | 6669篇 |
免费 | 544篇 |
国内免费 | 3篇 |
专业分类
7216篇 |
出版年
2022年 | 48篇 |
2021年 | 78篇 |
2020年 | 64篇 |
2019年 | 54篇 |
2018年 | 99篇 |
2017年 | 82篇 |
2016年 | 132篇 |
2015年 | 259篇 |
2014年 | 291篇 |
2013年 | 328篇 |
2012年 | 473篇 |
2011年 | 423篇 |
2010年 | 288篇 |
2009年 | 247篇 |
2008年 | 369篇 |
2007年 | 393篇 |
2006年 | 367篇 |
2005年 | 358篇 |
2004年 | 345篇 |
2003年 | 329篇 |
2002年 | 317篇 |
2001年 | 94篇 |
2000年 | 62篇 |
1999年 | 84篇 |
1998年 | 108篇 |
1997年 | 64篇 |
1996年 | 61篇 |
1995年 | 76篇 |
1994年 | 79篇 |
1993年 | 76篇 |
1992年 | 66篇 |
1991年 | 52篇 |
1990年 | 61篇 |
1989年 | 43篇 |
1988年 | 53篇 |
1987年 | 44篇 |
1986年 | 46篇 |
1985年 | 47篇 |
1984年 | 58篇 |
1983年 | 43篇 |
1982年 | 43篇 |
1981年 | 40篇 |
1980年 | 47篇 |
1979年 | 41篇 |
1978年 | 40篇 |
1977年 | 32篇 |
1974年 | 38篇 |
1972年 | 29篇 |
1970年 | 26篇 |
1969年 | 31篇 |
排序方式: 共有7216条查询结果,搜索用时 15 毫秒
131.
Specialized networks of movement detectors in the antero-inferior field of the eyes of the fruitfly, Drosophila melanogaster, and the housefly, Musca domestica, respond to upward (or downward) drift of the retinal images by excitation (or inhibition) of the lift-generating force of flight. The influence of the direction of pattern movement upon the altitude control response has been investigated under conditions of fixed flight in still air. Matched model analysis of the available response curves suggests the predominance of unidirectional movement detectors in these networks. Homologous wingbeat-inhibiting detectors in the specified fields of the eyes of the two species respond preferentially to pattern movement from antero-superior to postero-inferior. The arrangement of wingbeat-exciting detectors seems to follow different schemes: These detectors respond preferentially to movement from inferior to superior in Drosophila, and to movement from antero-inferior to postero-superior in Musca. The wingbeat-exciting network in Musca is restricted to a comparatively small antero-equatorial area of the specified fields of the eyes. The combination of the two types of detectors in this area establishes a powerful lift control system which is particularly sensitive to minute deviations from a given level of flight. 相似文献
132.
Kinocilia of epidermal sensory cells in fixed marine Turbellaria often terminate as flattened biconcave discs. The distal part of the ciliary axoneme curves back upon itself forming a 360 degree loop which is enveloped by the plasmalemma. In living animals this structure can be induced by the addition of sodium cacodylate, monobasic sodium phosphate, dibasic sodium phosphate, sucrose, calcium chloride, or formaldehyde to the sea water. Specimens treated with sodium chloride, glutaraldehyde, or osmium tetroxide do not show modified cilia. In animals prepared for EM at low temperature and with a buffered hypotonic fixative less kinocilia are modified than in animals treated with a buffered iso- or hypertonic fixative and at a higher temperature. It is assumed that the unusually shaped cilia, described as "paddle cilia" or "discocilia" in other invertebrates, do not represent a genuine but an artificial structure. 相似文献
133.
134.
Ulrich Heitkamp 《Hydrobiologia》1977,55(1):21-31
- At temperature levels from 10 to 25°C animals from resting eggs produce subitaneous eggs independent on temperature. In contrast animals from subitaneous eggs produce subitaneous eggs dependent on temperature. At a high rate subitaneous eggs are only formed at temperature levels above 20°C.
- Below 10°C no development occurs in the juveniles. At temperatures of 30/22°C (24.7°C) the first subitaneous eggs are formed after 6–9 days, at 14/9°C (10.7°C) they are formed after 34 days. At different temperature levels the developmental rate of the young is from 10.5 to 42 days. One generation extends over 16.5 (30/22°C) to 75 days (14/9°C). The average egg production is 10–20 subitaneous eggs or 30–60 resting eggs. The maximum egg production of one individual is 50 subitaneous eggs or 84 resting eggs. 50% of the animals have just formed resting eggs, before the juveniles are hatched. Resting eggs in the first egg-batch are formed 6–20 days later than subitaneous eggs. The duration of life is between 65 (30/22°C) and 140 days (19/13°C).
- Young worms in resting eggs have a dormance period of at least 15–30 days.
135.
In situ hybridization of cloned rRNA genes from Drosophila melanogaster to D. simulans metaphase chromosomes shows that in the tested wild type strains both sex chromosomes contain a nucleolus organizer region. Silver grain counts support the published data that the X chromosomal rRNA gene number is significantly higher than the Y chromosomal. 相似文献
136.
Nobuhiko Tada Shoji Kimura Yen Liu Benjamin A. Taylor Ulrich Hämmerling 《Immunogenetics》1981,13(6):539-546
Spleen cells from an SJL mouse immunized with 70'/3 cells, an established pre-B cell line, were fused with cells of the nonsecretor myeloma line NS.1. One established hybridoma cell line (clone K10.6) continuously secreted antibody that recognized a new antigenic specificity tentatively named Ly-m19. This newly found antigen is detectable on both T and B cells. Cytotoxicity assays reveal that 75 percent of the spleen and lymph-node cells, 35 percent of bone-marrow cells, and 15 percent of thymus cells reacted with antibody of clone K10.6. Strains expressing the specificity Ly-m19.1 are characterized by negative reactions and include the strains AKR, CE/J, RF/J, GR/A, SJL, P/J, BDP/J, and LG/J. All other strains so far tested are Ly-m19.2. This strain distribution pattern distinguishes Ly-m19 from any known murine lymphocyte alloantigen, but it parallels the Lyb-2
c
haplotype. Linkage test of a set of AKXL recombinant inbred strains revealed close linkage of Ly-m19 and Lyb-2 loci on mouse chromosome 4.Abbreviations used in this paper LPS
lipopolysaccharide
- B6
C57BL/6
- Con-A
concanavalin A
- MLC
mixed-lymphocyte culture
The prefix m (monoclonal) is used following a suggestion by Klein and co-workers (1979). 相似文献
137.
138.
139.
Jürgen Kunze Ulrich H. Frenzel Elke Hüttig Frank-Reiner Grosse Hans-Rudolf Wiedemann 《Human genetics》1977,35(2):237-240
Summary We report a newborn with incontinentia pigmenti Bloch-Sulzberger and male phenotype. Chromosome analysis revealed a Klinefelter's syndrome 47,XXY. These findings are compatible with the hypothesis of dominant sexlinked genes carried on the X-chromosome in this disease.
Zusammenfassung Wir berichten über ein neugeborenes Kind mit männlichem Phänotyp bei Incontinentia pigmenti Bloch-Sulzberger. Bei der klinischen Abklärung fand sich die Gonosomenaberration eines Klinefelter-Syndroms 47,XXY. Dieser Befund geht konform mit der Vermutung eines dominant X-gekoppelten Erbganges dieser seltenen Hauterkrankung.相似文献
140.