全文获取类型
收费全文 | 607435篇 |
免费 | 68688篇 |
国内免费 | 308篇 |
专业分类
676431篇 |
出版年
2018年 | 5220篇 |
2016年 | 7029篇 |
2015年 | 9739篇 |
2014年 | 11395篇 |
2013年 | 16312篇 |
2012年 | 18250篇 |
2011年 | 18392篇 |
2010年 | 12520篇 |
2009年 | 11265篇 |
2008年 | 16304篇 |
2007年 | 17006篇 |
2006年 | 15804篇 |
2005年 | 15334篇 |
2004年 | 15162篇 |
2003年 | 14636篇 |
2002年 | 14576篇 |
2001年 | 29290篇 |
2000年 | 29669篇 |
1999年 | 23298篇 |
1998年 | 7659篇 |
1997年 | 7969篇 |
1996年 | 7591篇 |
1995年 | 7174篇 |
1994年 | 7162篇 |
1993年 | 6894篇 |
1992年 | 19590篇 |
1991年 | 18835篇 |
1990年 | 18265篇 |
1989年 | 17685篇 |
1988年 | 16514篇 |
1987年 | 15531篇 |
1986年 | 14186篇 |
1985年 | 14238篇 |
1984年 | 11613篇 |
1983年 | 10155篇 |
1982年 | 7780篇 |
1981年 | 6867篇 |
1980年 | 6459篇 |
1979年 | 11401篇 |
1978年 | 8573篇 |
1977年 | 7908篇 |
1976年 | 7270篇 |
1975年 | 8115篇 |
1974年 | 8624篇 |
1973年 | 8608篇 |
1972年 | 7976篇 |
1971年 | 7167篇 |
1970年 | 6247篇 |
1969年 | 5993篇 |
1968年 | 5380篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
271.
J H Richardson L L Steinmetz S B Deutscher W A Bookless W L Schmelzinger 《Analytical biochemistry》1979,97(1):17-23
A synchronously pumped krypton ion dye laser fluorescence system is shown to provide tunable, polarized, subnanosecond pulses at high repetition rates, modest peak powers, and low energy. Such a source is uniquely suited to fluorescence investigations of biochemical mechanisms. Applications of this fluorescence excitation source to analysis, life-time determination, and depolarization effects are discussed. 相似文献
272.
Study of the posterior abdominal epidermis in hypophysectomized/thyroidectomized male and female tokays following surgery, and subsequent androgen therapy, indicates that, contrary to a previous model, all aspects of β-gland differentiation are under direct androgenic control. On the other hand, another epidermal specialization, the digital foot-pad, shows a pattern of histogenesis directly comparable to that of β-glands, but is unaffected by androgens. These data are discussed with respect to the evolution of glandular epidermal specializations in gekkonid lizards and the possible role of androgens in modifying the control of cell differentiation in lizard epidermis. 相似文献
273.
274.
B Rayner M Matsukura F Morvan J S Cohen J L Imbach 《Comptes rendus de l'Académie des sciences. Série III, Sciences de la vie》1989,310(3):61-64
Oligonucleotide analogs consisting exclusively of alpha-anomeric deoxynucleoside units bridged with phosphorothioate linkages have been synthesized and tested in vitro as antiviral agents against human immunodeficiency virus (HIV) in human T cells. Two 28-mers, an homopolymer alpha-S-dC28 and an oligomer alpha-S-anti-rev complementary to the initiation site of the regulatory viral gene rev exhibited antiviral activities comparable to those reported for the corresponding beta-anomeric phosphorothioate analogs. In contrast, a nuclease-resistant homopolymer, alpha-dC28 was inactive. Their preliminary results would indicate that the origin of oligonucleotide phosphorothioate anti-HIV activity is not exclusively correlated with their higher nuclease resistance. 相似文献
275.
276.
The photoacoustic spectroscopic studies of purple pigmented leaves revealed the occurrence of anthocyanins and betalains in
some local weed species growing on soils with low moisture levels. The pigmentation intensities were higher in C4 plants than in C3 plants. An inverse correlation was observed between pigmentation intensities and soil moisture levels.
This work is a part of the UNEP Research Project granted to Prof. D. O. Hall, UNEP Coordinator, Department of Plant Sciences,
King’s College; London. 相似文献
277.
S Kumar M Antony N K Mehrotra 《Biochemical and biophysical research communications》1984,125(3):967-973
Single cutaneous application of 12-O-tetradecanoyl-phorbol-13-acetate (TPA) increased epidermal oxidised glutathione reductase activity in adult mouse by almost 100%. Pretreatment of animals with vitamin A for a week resulted in 75% inhibition of TPA induced change in the enzyme activity which remained unaffected in skin treated with vitamin A alone. This biochemical change in skin induced by TPA and modulated by vitamin A has been discussed in relation to epidermal hyperplasia. 相似文献
278.
B. Boesiger 《Genetica》1982,59(2):99-111
The influence of inbreeding on several morphological characters as proboscis, wings, leg and palp segments was examined in strictly inbred lines of C. pipiens autogenicus, starting with females from a natural population. The results show the importance of ccological conditions, especially temperature, during larval development of the population. We report a progressive average size reduction from the second inbred generation. The length variability increases in practically all cases, depending on the degree of inbreeding, which is often more marked in certain organs. The symmetry regulation is strongly affected. We observe highly significant individual values in the highly inbred generations. The distribution values clearly mark a left/right disturbance. The progression of asymmetry as a function of the degree of inbreeding is more marked in certain organs in the two sexes. The results show the importance of the advantage of heterozygotes. 相似文献
279.
I V Kudriashova D B Logunov O S Papsuevich R I Kruglikov 《Biulleten' eksperimental'no? biologii i meditsiny》1985,99(1):5-7
Perfusion of the snail (Helix lucorum L.) CNS with DG-AVP (concentration 10(-6) M) in the course of low frequency intracellular stimulation (2-4-minute interval) of the defensive reflex command neurons led to an increase in the excitability. It was expressed both in the reduction of the spike generation latency, in the increased number of spikes in response to fixed stimuli, and in the activation of pacemaker potentials. If DG-AVP was added to the medium during endoneuronal habituation, there was no increase in the excitability. It is supposed that modification of the neuronal excitability may be caused by the DG-AVP effect on the pacemaker mechanism. 相似文献
280.
The influence of wilting on the levels of free proline, soluble proteins, reducing sugars, starch and on the activities of
nitrate reductase, invertase, amylase and pyrophosphatases have been studied in the leaf tissue of five cultivars of pearl
millet at their vegetative stage under pot culture conditions. The metabolic changes could not be correlated with the yield
behaviour of the cultivars under a drought condition in the field. 相似文献