全文获取类型
收费全文 | 659947篇 |
免费 | 61870篇 |
国内免费 | 513篇 |
专业分类
722330篇 |
出版年
2018年 | 10346篇 |
2017年 | 10006篇 |
2016年 | 10491篇 |
2015年 | 9180篇 |
2014年 | 10855篇 |
2013年 | 16038篇 |
2012年 | 19157篇 |
2011年 | 23957篇 |
2010年 | 17002篇 |
2009年 | 15731篇 |
2008年 | 20764篇 |
2007年 | 22839篇 |
2006年 | 16068篇 |
2005年 | 16044篇 |
2004年 | 15795篇 |
2003年 | 15627篇 |
2002年 | 15347篇 |
2001年 | 26772篇 |
2000年 | 26924篇 |
1999年 | 21157篇 |
1998年 | 7141篇 |
1997年 | 7511篇 |
1996年 | 7179篇 |
1995年 | 6720篇 |
1994年 | 6631篇 |
1993年 | 6532篇 |
1992年 | 17894篇 |
1991年 | 17564篇 |
1990年 | 17586篇 |
1989年 | 17184篇 |
1988年 | 16135篇 |
1987年 | 15304篇 |
1986年 | 14028篇 |
1985年 | 14664篇 |
1984年 | 11955篇 |
1983年 | 10332篇 |
1982年 | 7781篇 |
1981年 | 7016篇 |
1980年 | 6546篇 |
1979年 | 11416篇 |
1978年 | 8831篇 |
1977年 | 8312篇 |
1976年 | 7950篇 |
1975年 | 8819篇 |
1974年 | 9556篇 |
1973年 | 9440篇 |
1972年 | 9055篇 |
1971年 | 8313篇 |
1970年 | 6915篇 |
1969年 | 6687篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
992.
993.
The binding of norepinephrine (NE) to plasma proteins of fresh human blood obtained from healthy volunteers was studied by ultrafiltration at different NE concentrations and incubation times at 37 degrees C. At 1.7 nM L-[3H]-NE binding was approximately 25%. The binding was rapid and was not influenced by the incubation time. [3H]-NE could be dissociated from its binding sites by acid precipitation and, after HPLC, showed to be unchanged NE. No difference in NE binding was found between plasma collected in EGTA-GSH or heparin solution. There was no degradation of NE when incubated in plasma at 37 degrees C for 10 h, even without the addition of antioxidants. Therefore, in the present study, binding represented interaction of unchanged NE with plasma proteins. The whole plasma binding was saturable over the range of 0.66 nM to 0.59 mM of NE. Scatchard plot of specific binding revealed high-affinity sites with a Kd of 5.4 nM and a Bmax of 3.9 fmoles.mg-1 protein, and low-affinity sites with a Kd of 2.7 microM and a Bmax of 3.3 pmoles.mg-1 protein. Electrophoretic characterization of NE-binding proteins showed that about 60% of bound NE was associated to albumin, and 20% to prealbumin. NE binding to pure human plasma proteins was also studied using ultrafiltration. Scatchard analyses revealed a single class of very high-affinity binding sites for prealbumin (Kd 4.9 nM), a single class of binding sites for alpha 1-acid glycoprotein (Kd 54 microM) and two classes of binding sites for albumin with high (Kd 1.7 microM) and low (Kd 0.8 mM) affinities respectively. The main results obtained in this study - a) reversibility of NE binding, b) stability of free and bound NE in plasma, c) involvement of the prealbumin as a specific binding protein - point out to a specific transport for NE in human blood plasma. 相似文献
994.
The seasonal chronology of the events of the reproductive cycle, and changes in the structure and function of the primary and accessory organs of the male bent-winged bat, Miniopterus schreibersii, were studied at latitude 37 degrees S in temperate southeastern Australia. The testicular cycle commenced in late spring (November), and sperm appeared in the seminiferous tubules and epididymides in early fall (March). The cycle of the accessory sex gland complex generally paralleled the testicular cycle, reaching maximum hypertrophy at the time of insemination in late fall (April/May). Thereafter, the primary and secondary sex glands (except the ampullary gland) involuted as the animals entered winter torpor. However, a cauda epididymal store of sperm persisted until late spring, and sperm were often observed, as well, in the ampullary gland duct and alveoli throughout winter. This study has confirmed that male Miniopterus differs from other vespertilionids in that accessory gland activity declines following the fall breeding in keeping with the fact that, unlike in other vespertilionids, insemination, ovulation and conception are concurrent events in the fall in this species. The reduced secretory status of the Leydig cells and exceptionally low levels of circulating androgens throughout the year, in combination with the presence of viable epididymidal sperm for most of gestation, are all interesting features of this reproductive cycle. 相似文献
995.
996.
997.
998.
999.
O Chisaka K Araki T Ochiya T Tsurimoto W Hiranyawasitte-Attatippaholkun N Yanaihara K Matsubara 《Gene》1987,60(2-3):183-189
A fused gene containing 94% of the hepatitis B virus (HBV) open reading frame X was expressed in Escherichia coli, and its 17-kDa product was purified by ion-exchange chromatography. Antibody elicited against the X-gene product reacted with materials proximal to the nuclear membrane of a human hepatoblastoma cell line producing HBV particles. No such reaction was observed with the same cell line that did not produce HBV particles. 相似文献
1000.
Role of Thidiazuron (TDZ) in inducing adventitious organogenesis in Pongamia was studied. TDZ at different concentrations (0, 0.45, 2.27, 4.54, 6.71, 9.08, 11.35, 13.12 and 22.71 μM) were used for induction
of caulogenic bud formation in deembryonated cotyledon explants. Each cotyledon was cut into three segments and identified
as proximal, middle and distal. Duration of TDZ exposure, influence of the segment and orientation of the explant were studied.
TDZ at 11.35 μM concentration was optimum for the induction of shoots and rapid elongation. Shoots induced at higher concentration
elongated after several passages in growth regulator free medium, thereby extending the period of differentiation. Exposure
of the explant for 20 days yielded more number of buds than 10 days. Proximal segment of the cotyledon was more responsive.
Contact of abaxial surface in the medium was more effective and generated more buds than the adaxial side. Buds differentiated
and elongated on transfer to MS basal medium for 8–12 passages of 15 days each. Rooting and elongation of shoots was achieved
in charcoal supplemented half-strength MS medium. Rooted plantlets survived on transfer to sand soil mixture. The plants were
hardened and transferred to green house. This is the first report on in vitro regeneration of Pongamia pinnata via adventitious organogenesis using TDZ. This protocol may find application in studies in genetic transformation, isolation
of somaclonal variants and in induction of mutants. It also provides a system to study the inhibitory role of TDZ on shoot
differentiation. 相似文献