全文获取类型
收费全文 | 5971篇 |
免费 | 444篇 |
国内免费 | 413篇 |
出版年
2023年 | 59篇 |
2022年 | 69篇 |
2021年 | 131篇 |
2020年 | 147篇 |
2019年 | 176篇 |
2018年 | 167篇 |
2017年 | 135篇 |
2016年 | 176篇 |
2015年 | 190篇 |
2014年 | 264篇 |
2013年 | 358篇 |
2012年 | 217篇 |
2011年 | 286篇 |
2010年 | 244篇 |
2009年 | 322篇 |
2008年 | 294篇 |
2007年 | 329篇 |
2006年 | 302篇 |
2005年 | 295篇 |
2004年 | 281篇 |
2003年 | 233篇 |
2002年 | 197篇 |
2001年 | 189篇 |
2000年 | 149篇 |
1999年 | 165篇 |
1998年 | 147篇 |
1997年 | 126篇 |
1996年 | 119篇 |
1995年 | 128篇 |
1994年 | 111篇 |
1993年 | 91篇 |
1992年 | 96篇 |
1991年 | 95篇 |
1990年 | 70篇 |
1989年 | 69篇 |
1988年 | 52篇 |
1987年 | 48篇 |
1986年 | 40篇 |
1985年 | 58篇 |
1984年 | 38篇 |
1983年 | 25篇 |
1982年 | 31篇 |
1981年 | 19篇 |
1980年 | 24篇 |
1979年 | 13篇 |
1978年 | 14篇 |
1977年 | 11篇 |
1976年 | 12篇 |
1975年 | 4篇 |
1973年 | 6篇 |
排序方式: 共有6828条查询结果,搜索用时 15 毫秒
21.
《Molecular & cellular proteomics : MCP》2020,19(3):444-455
Highlights
- •Human spermatozoa possess cells of poor morphology that lack nuclear integrity.
- •These cells can be isolated by density separation.
- •Mass spectrometry reveals their nuclei contain excess protein.
- •TOP2A is a promising marker of this poor nuclear development.
22.
D. Stoyan 《Biometrical journal. Biometrische Zeitschrift》1985,27(4):411-425
This paper presents methods for the stereological analysis of spatial fibre systems on the base of planar or thin sections. Under the assumption that the cross-section figures of the tubular fibres can be measured, the orientation distribution of the fibre system and its line density Lv can be determined from one section only and without distributional assumptions. A simple way to study the degree of randomness of fibre systems consists in the statistical analysis of the point pattern of centres of intersection figures. More sophisticated methods are of stereological nature and yield the spatial reduced second moment measure. Similarly also correlations between two fibre systems can be quantified. The methods are demonstrated by two examples concerning samples of human brain. 相似文献
23.
24.
25.
Ihsan ul Haq C. Cáceres J. Hendrichs P. E. A. Teal C. Stauffer A. S. Robinson 《Entomologia Experimentalis et Applicata》2010,136(1):21-30
The effect of access to dietary protein (P) (hydrolyzed yeast) and/or treatment with a juvenile hormone analogue, methoprene (M), (in addition to sugar and water) on male aggregation (lekking) behaviour and mating success was studied in a laboratory strain of the melon fly, Bactrocera cucurbitae (Coquillett) (Diptera: Tephritidae). Six‐day‐old males were treated with (1) protein and methoprene (M+P+), (2) only protein (M?P+), or (3) only methoprene (M+P?), and compared with 14‐day‐old sexually mature untreated males (M?P?). The lekking behaviour of the four groups of males when competing for virgin sexually mature females (14 –16 days old) was observed in field cages. The following parameters were measured at male aggregations: lek initiation, lek participation, males calling, male–male interaction, female acceptance index, and mating success. For all these parameters, the M+P+ males significantly outperformed the other males. Moreover, for all parameters, there was a similar trend with M+P+ > M?P+ > M?P? > M+P?. More M+P+ males called and initiated and participated in lek activities than all other types of male, which resulted in higher mating success. They had also fewer unsuccessful copulation attempts than their counterparts. Whereas treatment with methoprene alone had a negative effect in young males with only access to sugar, access to dietary protein alone significantly improved young male sexual performance; moreover, the provision of methoprene together with protein had a synergistic effect, improving further male performance at leks. The results are of great relevance for enhancing the application of the sterile insect technique (SIT) against this pest species. The fact that access to dietary protein and treatment of sterile males with methoprene improves mating success means that SIT cost‐effectiveness is increased, as more released males survive to sexual maturity. 相似文献
26.
Storing the eggs of T. pisiformis for periods of 0 to 9 days at a temperature of 36–38°C and relative humidity of 87–93 % revealed at least 4 stages in the ageing process. Firstly, a stage in which eggs hatched and activated in vitro and were also fully infective for rabbits. Secondly, a stage in which eggs hatched and activated in vitro but underwent only partial development in rabbits. Thirdly, a stage in which eggs hatched and activated in vitro, and presumably therefore in vivo, but no evidence of infection could be found when they were fed to rabbits. Fourthly, a stage in which eggs either did not hatch, or if they did hatch, the oncosphere was rapidly digested. In vitro techniques for assessing viability of T. pisiformis eggs were not a reliable guide to their infectivity for rabbits. ‘Senescent’ eggs, that is eggs which produced evidence of early infection in rabbits but did not complete their development to cysticerci, failed to produce immunity to challenge infection with T. pisiformis eggs. 相似文献
27.
The measurement of the ATP content of fresh semen is as accurate as the estimation of sperm motility by conventional methods in discriminating between semen of fertile versus subfertile men. The ATP content of frozen thawed donor semen is correlated with the probability of conception per cycle of insemination. Exact quantification of cytotoxic sperm antibodies in serum is possible with the adenosine-triphosphate-release-cytotoxicity test, since measurement is free of the bias of microscopic examination. The procedure has been simplified by testing only one serum dilution and calculating the ‘sperm toxicity index’. 相似文献
28.
This study compared Pundamilia nyererei and Pundamilia pundamilia males in routine metabolic rate (RR) and in the metabolic costs males pay during territorial interactions (active metabolic rate, RA). Pundamilia nyererei and P. pundamilia males housed in social isolation did not differ in RR. In contrast to expectation, however, P. nyererei males used less oxygen than P. pundamilia males, for a given mass and level of agonistic activity. This increased metabolic efficiency may be an adaptation to limit the metabolic cost that P. nyererei males pay for their higher rate of aggressiveness compared to P. pundamilia males. Thus, the divergence between the species in agonistic behaviour is correlated with metabolic differentiation. Such concerted divergence in physiology and behaviour might be widespread in the dramatically diverse cichlid radiations in East African lakes and may be an important factor in the remarkably rapid speciation of these fishes. The results did not support the hypothesis that higher metabolic rates caused a physiological cost to P. nyererei males that would offset their dominance advantage. 相似文献
29.
Caroline van Haaften-Day Peter Russell Susan Carr Lesley Wright 《In vitro cellular & developmental biology. Plant》1988,24(10):965-971
Summary A cell line derived from a human ovarian carcinosarcoma was established in tissue culture and in nude mice. Two sublines,
LDF and HDF, separated by discontinuous density centrifugation were also established from the parent line JoN. The cloning
efficiency of the JoN line was 21%. Morphologic features of adenocarcinoma cells characteristic of the parent JoN cells were
retained in the sublines and clones; all lines showed the same karyotype and DNA content (pseudodiploid and pseudotetraploid).
Keratin, as demonstrated immunohistochemically, was strongly expressed in the parent line JoN and the xenograft tumor, but
not at all in the LDF sublines and only moderately in the HDF sublines. Vimentin, however, was expressed in neither the parent
line JoN nor the xenograft tumor, but was present in both sublines. Transglutaminase and plasminogen activator activity was
high in the parent line JoN. Neither, sublines nor clones showed the same high enzyme activity as the parent line. It is concluded
that this human tumor line JoN is comprised of epithelial cells, capable of multidirectional differentiation. 相似文献
30.