全文获取类型
收费全文 | 9629篇 |
免费 | 899篇 |
国内免费 | 1篇 |
出版年
2023年 | 75篇 |
2022年 | 126篇 |
2021年 | 306篇 |
2020年 | 150篇 |
2019年 | 191篇 |
2018年 | 255篇 |
2017年 | 220篇 |
2016年 | 348篇 |
2015年 | 568篇 |
2014年 | 610篇 |
2013年 | 746篇 |
2012年 | 806篇 |
2011年 | 875篇 |
2010年 | 519篇 |
2009年 | 399篇 |
2008年 | 610篇 |
2007年 | 597篇 |
2006年 | 470篇 |
2005年 | 444篇 |
2004年 | 414篇 |
2003年 | 324篇 |
2002年 | 307篇 |
2001年 | 86篇 |
2000年 | 80篇 |
1999年 | 74篇 |
1998年 | 65篇 |
1997年 | 53篇 |
1996年 | 47篇 |
1995年 | 61篇 |
1994年 | 40篇 |
1993年 | 33篇 |
1992年 | 34篇 |
1991年 | 38篇 |
1990年 | 37篇 |
1989年 | 29篇 |
1988年 | 30篇 |
1987年 | 30篇 |
1986年 | 27篇 |
1985年 | 22篇 |
1984年 | 41篇 |
1983年 | 21篇 |
1982年 | 15篇 |
1981年 | 23篇 |
1980年 | 15篇 |
1978年 | 15篇 |
1977年 | 20篇 |
1976年 | 18篇 |
1975年 | 19篇 |
1974年 | 15篇 |
1973年 | 15篇 |
排序方式: 共有10000条查询结果,搜索用时 15 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.
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
110.
Adam Sun Eric B. Grossman Michael Lombardi Steven C. Hebert 《The Journal of membrane biology》1991,120(1):83-94
Summary Experiments were performed usingin vitro perfused medullary thick ascending limbs of Henle (MTAL) and in suspensions of MTAL tubules isolated from mouse kidney to evaluate the effects of arginine vasopressin (AVP) on the K+ dependence of the apical, furosemide-sensitive Na+:Cl– cotransporter and on transport-related oxygen consumption (QO2). In isolated perfused MTAL segments, the rate of cell swelling induced by removing K+ from, and adding onemm ouabain to, the basolateral solution [ouabain(zero-K+)] provided an index to apical cotransporter activity and was used to evaluated the ionic requirements of the apical cotransporter in the presence and absence of AVP. In the absence of AVP cotransporter activity required Na+ and Cl–, but not K+, while in the presence of AVP the apical cotransporter required all three ions.86Rb+ uptake into MTAL tubules in suspension was significant only after exposure of tubules to AVP. Moreover,22Na+ uptake was unaffected by extracellular K+ in the absence of AVP while after AVP exposure22Na+ uptake was strictly K+-dependent. The AVP-induced coupling of K+ to the Na+:Cl– cotransporter resulted in a doubling in the rate of NaCl absorption without a parallel increase in the rate of cellular22Na+ uptake or transport-related oxygen consumption. These results indicate that arginine vasopressin alters the mode of a loop diuretic-sensitive transporter from Na+:Cl– cotransport to Na+:K+:2Cl– cotransport in the mouse MTAL with the latter providing a distinct metabolic advantage for sodium transport. A model for AVP action on NaCl absorption by the MTAL is presented and the physiological significance of the coupling of K+ to the apical Na+:Cl– cotransporter in the MTAL and of the enhanced metabolic efficiency are discussed. 相似文献