全文获取类型
收费全文 | 3887篇 |
免费 | 328篇 |
国内免费 | 1篇 |
出版年
2021年 | 39篇 |
2020年 | 21篇 |
2019年 | 30篇 |
2018年 | 34篇 |
2017年 | 46篇 |
2016年 | 70篇 |
2015年 | 117篇 |
2014年 | 150篇 |
2013年 | 184篇 |
2012年 | 203篇 |
2011年 | 195篇 |
2010年 | 150篇 |
2009年 | 148篇 |
2008年 | 211篇 |
2007年 | 227篇 |
2006年 | 208篇 |
2005年 | 211篇 |
2004年 | 227篇 |
2003年 | 221篇 |
2002年 | 239篇 |
2001年 | 57篇 |
2000年 | 41篇 |
1999年 | 48篇 |
1998年 | 81篇 |
1997年 | 58篇 |
1996年 | 47篇 |
1995年 | 67篇 |
1994年 | 50篇 |
1993年 | 52篇 |
1992年 | 48篇 |
1991年 | 46篇 |
1990年 | 27篇 |
1989年 | 45篇 |
1988年 | 34篇 |
1987年 | 32篇 |
1986年 | 23篇 |
1985年 | 43篇 |
1984年 | 44篇 |
1983年 | 25篇 |
1982年 | 38篇 |
1981年 | 35篇 |
1980年 | 19篇 |
1978年 | 20篇 |
1977年 | 20篇 |
1976年 | 33篇 |
1975年 | 28篇 |
1974年 | 23篇 |
1973年 | 20篇 |
1971年 | 21篇 |
1968年 | 19篇 |
排序方式: 共有4216条查询结果,搜索用时 31 毫秒
921.
4-Bromophenacyl bromide at a concentration of 50 microM does not inhibit phospholipase A2 activity in liver macrophages. Rather, this compound increases the amount of radioactivity released from [3H]arachidonate-prelabeled Kupffer cells and leads to the formation of small amounts of thromboxane, prostaglandin D2 and prostaglandin E2. Also the zymosan-induced formation of thromboxane and prostaglandin E2 from endogenous sources which is thought to involve phospholipase A2 remains unaffected in the presence of this compound. The generation of superoxide and the formation of prostaglandin D2 from arachidonate and after stimulation of the cells with zymosan, however, are blocked by 4-bromophenacyl bromide. Furthermore, this compound suppresses the incorporation of externally added arachidonate into membrane lipids of the cells. 4-Bromophenacyl bromide seems, therefore, not to be a useful tool to demonstrate the involvement of phospholipase A2 in complex biological systems. 相似文献
922.
The regulatory properties of four enzymes (homocitrate synthase, -aminoadipate reductase, saccharopine reductase, saccharopine dehydrogenase) involved in the lysine biosynthesis of Pichia guilliermondii were investigated and compared with the regulatory patterns found in other yeast species. The first enzyme of the pathway, homocitrate synthase, is feedback-inhibited by L-lysine. Some other amino acids (-aminoadipate, glutamate, tryptophan, leucine) and lysine analogues are also inhibitors of one or more enzymes. It is shown that only the synthesis of homocitrate synthase is weakly repressed by L-lysine. 相似文献
923.
924.
Protein recovery by continuous flotation 总被引:2,自引:0,他引:2
Summary Bovine serum albumin (BSA) was recovered from aqueous solutions by foam flotation. The protein concentrations in foam liquid C
S, in feed C
Pand in residue C
Rwere determined. The protein enrichment C
S/CPand the separation C
S/CRas well as the protein fraction in the foam liquid % BSA and foam liquid volume flow were determined as functions of the medium properties, operational conditions, and equipment parameters as well as concentrations of solid particles. At low protein concentrations in feed (e.g., C
P=40 mg · l-1), and at 40° C, high performance was attained (C
X=2,000 mg · l-1, C
R=4.4 mg · l-1, C
S/CP=50, C
S/CR=450, 90% BSA. Continuous foam flotation is an efficient procedure for the recovery of low concentrations of proteins from liquid cultures.Abbreviations BSA
bovine serum albumine
-
C
P
protein concentration in feed (mg · l-1)
-
C
R
protein concentration in residue (mg · l-1)
-
C
S
protein concentration in foam liquid (mg · l-1)
-
C
S/CR
protein separation (-)
-
C
S/CP
protein enrichment (-)
-
V
P
feed rate (ml · min-1)
-
V
R
residue flow rate (ml · min-1)
-
V
S
foam liquid volume flow (ml · min-1)
-
N
number of theoretical stages in an ideal cascade (-)
-
temperature (° C)
-
mean residence time (min) 相似文献
925.
Methanogenesis in the hypersaline Solar Lake (Sinai) 总被引:2,自引:0,他引:2
Dieter Giani Luise Giani Yehuda Cohen Wolfgang E. Krumbein 《FEMS microbiology letters》1984,25(2-3):219-224
Abstract Enrichment studies on microbial mat sediments (potential stromatolites) from the hypersaline Solar Lake (Sinai) indicated high numbers of methanogenic bacteria (up to 105 ml−1 sediment) in spite of the high sulfate reduction rate, sulfate concentration and salinity. Among H2 /CO2 , acetate and monomethylamine, the methylated amine was the preferred substrate. The predominant species enriched was a Methanosarcina sp. The findings indicate that methanogenic bacteria play an important role in hypersaline sulfate-enriched anoxic sediments and stromatolithic microbial mats. 相似文献
926.
Seedlings of red radish (Raphanus sativus L. var. sativus) accumulated high amounts of free malic acid and sinapoylmalate, when grown on nitrate as the sole N-source. In the presence of ammonium (NO
3
–
: NH
4
+
, 1:2) both metabolites failed to accumulate, and the levels of arginine, asparagine, glutamine, histidine, and serine were greatly increased. The extractable activity of 1-sinapoylglucose: l-malate sinapoyltransferase, an enzyme which plays a key role in channelling malic acid into the sinapic-acid metabolism of this plant, was positively correlated with the malic-acid level in cotyledons. The possibility is discussed that free malic acid might be the likely candidate for regulating the activity of 1-sinapoylglucose: l-malate sinapoyltransferase.Abbreviation SMT
sinapoylglucose: L-malate sinapoyltransferase 相似文献
927.
Dieter Fritze Shankar K. Nayak Yosef H. Pilch 《Cancer immunology, immunotherapy : CII》1980,9(4):255-263
Summary Using leukocyte adherence inhibition (LAI) tests, we studied the activity of xenogeneic immune RNA (I-RNA) extracted from the spleen and lymph nodes of sheep after immunization with human breast carcinoma tissue or keyhole limpet hemocyanin (KLH) in inducing lymphocytes from normal healthy donors to mediate immune responses in vitro. Mononuclear cells isolated from venous blood of normal donors, depleted of monocytes and, in some experiments, separated into T cells and non-T cells, were incubated with and without anti-breast carcinoma I-RNA or anti-KLH I-RNA for 20 min at 37° C. Then, lymphocyte adherence was determined by a Coulter counter method in the presence of 3 M KCl extracts of breast carcinoma tissues, control tissue, or KLH. Following incubation with anti-breast carcinoma I-RNA, the adherence of lymphocytes from normal donors was found to be inhibited only in the presence of breast carcinoma extracts. Following incubation with anti-KLH I-RNA, lymphocyte adherence was inhibited only in the presence of KLH. The principal effector cells involved appeared to be T lymphocytes. I-RNA treatment with RNase, but not with DNase or pronase, completely abrogated the LAI responses. In a blind study utilizing coded samples of xenogeneic and allogeneic I-RNA of unknown origin, samples containing activity against breast cancer extracts were identified correctly by LAI.
Abbreviations used: I-RNA, immune RNA; LAI, leukocyte adherence inhibition; KLH, Keyhole limpet hemocyanin; PBS, phosphate buffered saline; RNase, ribonuclease; DNase, deoxyribonuclease 相似文献
928.
929.
Ottmar Kullmer Stefano Benazzi Luca Fiorenza Dieter Schulz Stefan Bacso Olaf Winzen 《American journal of physical anthropology》2009,139(4):600-605
Information about food ingestion and mastication behavior during the lifespan of an individual is encoded in the dental occlusal wear pattern. To decode this information, we describe a new method called occlusal fingerprint analysis (OFA). Structural parameters of wear facets on the occlusal surface of teeth are quantified from digitized casts for the interpretation of occlusal aspects. The OFA provides an individual three‐dimensional dental occlusal compass that indicates the major pathways of interaction between antagonists, revealing information about development, spatial position, and enlargement of wear facets. Humans develop a very similar overall pattern of crown contacts, although specific characteristics of wear facets reflect an individual's occlusal relationships and masticatory behavior. We hypothesize that the wear pattern is a unique character and therefore valuable for individual identification. Furthermore we suggest that OFA, when further developed, may be useful for identification of behavioral, biological, and chemical factors affecting crown morphology. Am J Phys Anthropol, 2009. © 2009 Wiley‐Liss, Inc. 相似文献
930.
René Csuk Alexander Barthel Ralph Kluge Dieter Ströhl 《Bioorganic & medicinal chemistry》2010,18(20):7252-7259
Several novel betulin derivatives were prepared and evaluated for their antitumor activity. 3-O-Acetylbetulinic aldehyde served as an ideal starting material for the synthesis of 28-acetylenic derivatives. These compounds were further transformed into pyrazoles and 1,2,3-triazoles. Also, the synthesis of 3-amino substituted butenolides was carried out. The compounds were screened for their antitumor activity in a panel of 15 human cancer cell lines in a sulforhodamine B (SRB) assay. Several compounds showed a noteworthy antitumor activity. In addition, the possibility of encapsulation into liposomes was examined, thereby resulting in an increased cytotoxicity. The results from a trypan-blue test and from DNA laddering provided evidence for an apoptotic cell death. 相似文献