全文获取类型
收费全文 | 9538篇 |
免费 | 884篇 |
国内免费 | 1篇 |
出版年
2023年 | 63篇 |
2022年 | 30篇 |
2021年 | 300篇 |
2020年 | 149篇 |
2019年 | 191篇 |
2018年 | 256篇 |
2017年 | 223篇 |
2016年 | 348篇 |
2015年 | 570篇 |
2014年 | 611篇 |
2013年 | 745篇 |
2012年 | 807篇 |
2011年 | 877篇 |
2010年 | 518篇 |
2009年 | 401篇 |
2008年 | 611篇 |
2007年 | 600篇 |
2006年 | 470篇 |
2005年 | 443篇 |
2004年 | 412篇 |
2003年 | 321篇 |
2002年 | 307篇 |
2001年 | 85篇 |
2000年 | 78篇 |
1999年 | 75篇 |
1998年 | 64篇 |
1997年 | 53篇 |
1996年 | 44篇 |
1995年 | 61篇 |
1994年 | 41篇 |
1993年 | 34篇 |
1992年 | 32篇 |
1991年 | 40篇 |
1990年 | 37篇 |
1989年 | 30篇 |
1988年 | 29篇 |
1987年 | 28篇 |
1986年 | 27篇 |
1985年 | 24篇 |
1984年 | 41篇 |
1983年 | 22篇 |
1982年 | 15篇 |
1981年 | 23篇 |
1980年 | 16篇 |
1978年 | 16篇 |
1977年 | 20篇 |
1976年 | 20篇 |
1975年 | 19篇 |
1974年 | 17篇 |
1973年 | 15篇 |
排序方式: 共有10000条查询结果,搜索用时 734 毫秒
101.
In order to determine the significance of the C-6 carboxyl group for the biological activity gibberellin A3, 6-epigibberellin A3, 7-norgibberellin A3, 6-methyl-7-norgibberellin A3, and 7-homogibberellin A3 were studied using dwarf pea, dwarf maize, dwarf rice, dwarf barley and -amylase bioassays. All gibberellin A3(GA3)derivatives tested were considerably less active than GA3. In all biossays, 6-epi-GA3 showed a low activity of the same order, whereas 6-methyl-7-nor-GA3 was inactive. Surprisingly, 7-nor-GA3 had some activity in the dwarf rice (root application), dwarf barley, and -amylase bioassay, in contrary to its low potency in the dwarf pea, dwarf maize, and dwarf rice (micro drop) bioassay. 7-Homo-GA3 was primarily active in the dwarf maize, dwarf barley and dwarf rice bioassay. It also caused antigibberellin effects in dwarf rice. The results demonstrate that the C-6 carboxyl group is not absolutely essential for biological activity of gibberellins. The different activities of 7-nor-GA3 observed in the various test systems may indicate that the C-6 carboxyl group is a structural requirement more for uptake and/or transport processes than for receptor affinity.Abbreviation GA3
gibberellic acid 相似文献
102.
103.
104.
105.
106.
Mag. rer. nat. Alois Lametschwandtner Peter Simonsberger Hans Adam 《Cell and tissue research》1977,180(4):433-442
The angioarchitecture of the neural stalk and the encephaloposthypophysial portal system of the hypophysis of the toad, Bufo bufo (L.), was studied using three different methods. The neural stalk is mainly supplied by branches of the arteria infundibularis superficialis which form a widemeshed vascular network. Dorsally this network continues into the plexus of the pars nervosa. The vascularization of the pars nervosa is made up of the encephalo-posthypophysial portal system. This portal system consists of a hypothalamic branch (=portion), a mesencephalic and a mesencephalicbulbar branch (=portion). The hypothalamic branch was found to drain the pars ventralis of the tuber cinereum as well as more dorsal regions of the diencephalon. The mesencephalic-bulbar trunk enters the hypothalamic branch. The resulting common stem of the encephalo-posthypophysial portal vein the curves around the retroinfundibular communicating artery, crosses its ventral side and runs caudally. The secondary capillary plexus of the pars nervosa is characterized by well defined capillary plexus of the pars nervosa is characterized by well defined capillary networks which are located at the periphery of the parenchyma of the pars nervosa, thus forming a rostral, dorsal and ventro-caudal net. The central region of the parenchyma of the pars nervosa is supplied only by main branches of the encephalo-postpophysial portal vein. The venous drainage of the pars nervosa is via the vena hypophysea transversa. 相似文献
107.
Adam Zipp Irwin D. Kuntz Thomas L. James 《Archives of biochemistry and biophysics》1977,178(2):435-441
The dependence of the water proton magnetic resonance spin-lattice relaxation rate (T1??1) in the rotating frame on the strength of the spin-locking (H1) field has been investigated for packed oxy and deoxy normal and sickle erythrocytes at temperatures from 9 to 40 °C. The T1??1 of oxy or deoxy normal erythrocytes shows no dependence on H1 up to ~7 G at any temperature studied. On the other hand, T1??1 decreases from about 40 s?1 to 15 s?1 (H1 from 0 to ~7 G) for deoxygenated packed sickle cells at 40 °C. The magnitude of this variation of T1??1 with H1 decreases with decreasing temperature. Oxy packed sickle cells also show a dependence of T1??1 on H1 but the magnitude is <10% of that of the deoxygenated samples. These results suggest that water proton T1??1 measurements are a sensitive probe of hemoglobin S polymerization and provide a novel technique for the study of slow water motions in these systems. The T1??1 results are compared with low frequency T1?1 results of other investigators on hemoglobin S solutions. Analysis of the data suggests that water proton motions with correlation times of the order of 10?5 s are present in the deoxygenated sickle cell samples at temperatures above 10 °C. 相似文献
108.
109.
A Ayala M M Perrin P Wang W Ertel I H Chaudry 《Journal of immunology (Baltimore, Md. : 1950)》1991,147(12):4147-4154
Studies indicate that simple hemorrhage produces a profound depression of cell-mediated immunity, thereby contributing to an enhanced susceptibility to septic challenge in the host. However, it remains unknown whether or not the macrophages' cytotoxic capacity is altered after hemorrhage. To study this, C3H/HeN mice were bled to and maintained at a blood pressure of 35 mm Hg for 60 min, and adequately resuscitated. Mice were then killed at 2 or 24 h after hemorrhage to obtain peritoneal macrophage, splenic macrophage, and Kupffer cells. Cytotoxicity was assessed by determining the capacity of these macrophages to lyse [3H]TdR labeled WEHI-164 clone 13 or P815 tumor target cells (WEHI-164, sensitive to both soluble and cell-associated TNF vs P815 cells, insensitive to soluble TNF). Peritoneal and splenic macrophages from hemorrhaged animals exhibited a significantly reduced cytotoxic capacity, whereas Kupffer cells' ability to kill the target cells was enhanced. Similarly, the Kupffer cells' capacity to release TNF and IL-1, as well as express cell-associated forms of this cytokine are significantly enhanced on macrophages isolated 2 h after hemorrhage, whereas peritoneal macrophages are not. Furthermore, antibodies directed at mouse TNF but not against murine IL-1 alpha or murine IL-6 were able to oblate the enhanced target cell lysis of unfixed, as well as paraformaldehyde fixed (metabolically inactive) Kupffer cells. Studies using inhibitors (GN-monomethyl-arginine, superoxide dismutase, catalase, and ibuprofen) of other TNF-inducible mechanisms of target cell killing indicated that only the inhibition of the release of reactive nitrogen consistently depressed the cytotoxic capacity of Kupffer cells from hemorrhaged mice. Thus, the increased Kupffer cell cytotoxicity from hemorrhaged mice is most likely mediated through the expression of cell-associated TNF and the release of reactive nitrogen. 相似文献
110.
Summary We have recently shown that stimulation of electrogenic HCO
3
–
secretion is accompanied by a simultaneous increase in short-circuit current (I
sc, equivalent to HCO
3
–
secretion rate under these conditions), apical membrane capacitance (C
a
, proportional to membrane area), and apical membrane conductance (G
a
, proportional to membrane ionic permeability). The current experiments were undertaken to explore the ionic basis for the increase inG
a
and the possibility that the rate of electrogenic HCO
3
–
secretion is regulated by changes inG
a
. Membrane electrical parameters were measured using impedance-analysis techniques before and after stimulation of electrogenic HCO
3
–
secretion with cAMP in three solutions which contained different chloride concentrations. In another series of experiments, the effects of an anion channel blocker, anthracene-9-carboxylic acid (9-AA), were measured after stimulation of electrogenic HCO
3
–
secretion with cAMP. The major conclusions are: (i) a measurable apical Cl– conductance exists in control hemibladders; (ii) the transport-associated increase inG
a
includes a Cl–-conductive component; (iii)G
a
also appears to reflect a HCO
3
–
conductance; (iv) the relative magnitudes of the apical membrane conductances to Cl– and HCO
3
–
are similar; (v) 9-AA reducesG
a
andI
sc appear cAMP-stimulated hemibladders; and (vi) alterations inI
sc appear to be mediated by changes inG
a
. 相似文献